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diff --git a/open_issues/performance/ipc_virtual_copy.mdwn b/open_issues/performance/ipc_virtual_copy.mdwn deleted file mode 100644 index 9708ab96..00000000 --- a/open_issues/performance/ipc_virtual_copy.mdwn +++ /dev/null @@ -1,395 +0,0 @@ -[[!meta copyright="Copyright © 2011 Free Software Foundation, Inc."]] - -[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable -id="license" text="Permission is granted to copy, distribute and/or modify this -document under the terms of the GNU Free Documentation License, Version 1.2 or -any later version published by the Free Software Foundation; with no Invariant -Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license -is included in the section entitled [[GNU Free Documentation -License|/fdl]]."]]"""]] - -IRC, freenode, #hurd, 2011-09-02: - - <slpz> what's the usual throughput for I/O operations (like "dd - if=/dev/zero of=/dev/null") in one of those Xen based Hurd machines - (*bber)? - <braunr> good question - <braunr> slpz: but don't use /dev/zero and /dev/null, as they don't have - anything to do with true I/O operations - <slpz> braunr: in fact, I want to test the performance of IPC's virtual - copy operations - <braunr> ok - <slpz> braunr: sorry, the "I/O" was misleading - <braunr> use bs=4096 then i guess - <slpz> bs > 2k - <braunr> ? - <slpz> braunr: everything about 2k is copied by vm_map_copyin/copyout - <slpz> s/about/above/ - <slpz> braunr: MiG's stubs check for that value and generate complex (with - out_of_line memory) messages if datalen is above 2k, IIRC - <braunr> ok - <braunr> slpz: found it, thanks - <tschwinge> tschwinge@strauss:~ $ dd if=/dev/zero of=/dev/null bs=4k & p=$! - && sleep 10 && kill -s INFO $p && sleep 1 && kill $p - <tschwinge> [1] 13469 - <tschwinge> 17091+0 records in - <tschwinge> 17090+0 records out - <tschwinge> 70000640 bytes (70 MB) copied, 17.1436 s, 4.1 MB/s - <tschwinge> Note, however 10 s vs. 17 s! - <tschwinge> And this is slow compared to heal hardware: - <tschwinge> thomas@coulomb:~ $ dd if=/dev/zero of=/dev/null bs=4k & p=$! && - sleep 10 && kill -s INFO $p && sleep 1 && kill $p - <tschwinge> [1] 28290 - <tschwinge> 93611+0 records in - <tschwinge> 93610+0 records out - <tschwinge> 383426560 bytes (383 MB) copied, 9.99 s, 38.4 MB/s - <braunr> tschwinge: is the first result on xen vm ? - <tschwinge> I think so. - <braunr> :/ - <slpz> tschwinge: Thanks! Could you please try with a higher block size, - something like 128k or 256k? - <tschwinge> strauss is on a machine that also hosts a buildd, I think. - <braunr> oh ok - <pinotree> yes, aside either rossini or mozart - <tschwinge> And I can confirm that with dd if=/dev/zero of=/dev/null bs=4k - running, a parallel sleep 10 takes about 20 s (on strauss). - -[[open_issues/time]] - - <braunr> slpz: i'll set up xen hosts soon and can try those tests while - nothing else runs to have more accurate results - <tschwinge> tschwinge@strauss:~ $ dd if=/dev/zero of=/dev/null bs=256k & - p=$! && sleep 10 && kill -s INFO $p && sleep 1 && kill $p - <tschwinge> [1] 13482 - <tschwinge> 4566+0 records in - <tschwinge> 4565+0 records out - <tschwinge> 1196687360 bytes (1.2 GB) copied, 13.6751 s, 87.5 MB/s - <braunr> slpz: gains are logarithmic beyond the page size - <tschwinge> thomas@coulomb:~ $ dd if=/dev/zero of=/dev/null bs=256k & p=$! - && sleep 10 && kill -s INFO $p && sleep 1 && kill $p - <tschwinge> [1] 28295 - <tschwinge> 6335+0 records in - <tschwinge> 6334+0 records out - <tschwinge> 1660420096 bytes (1.7 GB) copied, 9.99 s, 166 MB/s - <tschwinge> This time a the sleep 10 decided to take 13.6 s. - ``Interesting.'' - <slpz> tschwinge: Thanks again. The results for the Xen machine are not bad - though. I can't obtain a throughput over 50MB/s with KVM. - <tschwinge> slpz: Want more data (bs)? Just tell. - <braunr> slpz: i easily get more than that - <braunr> slpz: what buffer size do you use ? - <slpz> tschwinge: no, I just wanted to see if Xen has an upper limit beyond - KVM's. Thank you. - <slpz> braunr: I try with different sizes until I find the maximum - throughput for a certain amount of requests (count) - <slpz> braunr: are you working with KVM? - <braunr> yes - <braunr> slpz: my processor is a model name : Intel(R) Core(TM)2 Duo - CPU E7500 @ 2.93GHz - <braunr> Linux silvermoon 2.6.32-5-amd64 #1 SMP Tue Jun 14 09:42:28 UTC - 2011 x86_64 GNU/Linux - <braunr> (standard amd64 squeeze kernel) - <slpz> braunr: and KVM's version? - <braunr> squeeze (0.12.5) - <braunr> bbl - <gnu_srs> 212467712 bytes (212 MB) copied, 9.95 s, 21.4 MB/s on kvm for me! - <slpz> gnu_srs: which block size? - <gnu_srs> 4k, and 61.7 MB/s with 256k - <slpz> gnu_srs: could you try with 512k and 1M? - <gnu_srs> 512k: 56.0 MB/s, 1024k: 40.2 MB/s Looks like the peak is around a - few 100k - <slpz> gnu_srs: thanks! - <slpz> I've just obtained 1.3GB/s with bs=512k on other (newer) machine - <braunr> on which hw/vm ? - <slpz> I knew this is a cpu-bound test, but I couldn't imagine faster - processors could make this difference - <slpz> braunr: Intel(R) Core(TM) i5 CPU 650 @ 3.20GHz - <slpz> braunr: KVM - <braunr> ok - <braunr> how much time did you wait before reading the result ? - <slpz> that was 20x times better than the same test on my Intel(R) - Core(TM)2 Duo CPU T7500 @ 2.20GHz - <slpz> braunr: I've repeated the test with a fixed "count" - <gnu_srs> My box is: Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz: Max - is 67 MB/s around 140k block size - <braunr> yes but how much time did dd run ? - <gnu_srs> 10 s plus/minus a few fractions of a second, - <braunr> try waiting 30s - <slpz> braunr: didn't check, let me try again - <braunr> my kvm peaks at 130 MiB/s with bs 512k / 1M - <gnu_srs> 2029690880 bytes (2.0 GB) copied, 30.02 s, 67.6 MB/s, bs=140k - <braunr> gnu_srs: i'm very surprised with slpz's result of 1.3 GiB/s - <slpz> braunr: over 60 s running, same performance - <braunr> nice - <braunr> i wonder what makes it so fast - <braunr> how much cache ? - <gnu_srs> Me too, I cannot get better values than around 67 MB/s - <braunr> gnu_srs: same questions - <slpz> braunr: 4096KB, same as my laptop - <braunr> slpz: l2 ? l3 ? - <gnu_srs> kvm: cache=writeback, CPU: 4096 KB - <braunr> gnu_srs: this has nothing to do with the qemu option, it's about - the cpu - <slpz> braunr: no idea, it's the first time I touch this machine. I going - to see if I find the model in processorfinder - <braunr> under my host linux system, i get a similar plot, that is, - performance drops beyond bs=1M - <gnu_srs> braunr: OK, bu I gave you the cache size too, same as slpz. - <braunr> i wonder what dd actually does - <braunr> read() and writes i guess - <slpz> braunr: read/write repeatedly, nothing fancy - <braunr> slpz: i don't think it's a good test for virtual copy - <braunr> io_read_request, vm_deallocate, io_write_request, right - <braunr> slpz: i really wonder what it is about i5 that improves speed so - much - <slpz> braunr: me too - <slpz> braunr: L2: 2x256KB, L3: 4MB - <slpz> and something calling "SmartCache" - <gnu_srs> slpz: where did you find these values? - <slpz> gnu_srs: ark.intel.com and wikipedia - <gnu_srs> aha, cpuinfo just gives cache size. - <slpz> that "SmartCache" thing seems to be just L2 cache sharing between - cores. Shouldn't make a different since we're using only one core, and I - don't see KVM hooping between them. - <manuel> with bs=256k: 7004487680 bytes (7.0 GB) copied, 10 s, 700 MB/s - <manuel> (qemu/kvm, 3 * Intel(R) Xeon(R) E5504 2GHz, cache size 4096 KB) - <slpz> manuel: did you try with 512k/1M? - <manuel> bs=512k: 7730626560 bytes (7.7 GB) copied, 10 s, 773 MB/s - <manuel> bs=1M: 7896825856 bytes (7.9 GB) copied, 10 s, 790 MB/s - <slpz> manuel: those are pretty good numbers too - <braunr> xeon processor - <gnu_srs> lshw gave me: L1 Cache 256KiB, L2 cache 4MiB - <slpz> sincerely, I've never seen Hurd running this fast. Just checked - "uname -a" to make sure I didn't take the wrong image :-) - <manuel> for bs=256k, 60s: 40582250496 bytes (41 GB) copied, 60 s, 676 MB/s - <braunr> slpz: i think you can assume processor differences alter raw - copies too much to get any valuable results about virtual copy operations - <braunr> you need a specialized test program - <manuel> and bs=512k, 60s, 753 MB/s - <slpz> braunr: I'm using the mach_perf suite from OSFMach to do the - "serious" testing. I just wanted a non-synthetic test to confirm the - readings. - -[[!taglink open_issue_gnumach]] -- have a look at *mach_perf*. - - <braunr> manuel: how much cache ? 2M ? - <braunr> slpz: ok - <braunr> manuel: hmno, more i guess - <manuel> braunr: /proc/cpuinfo says cache size : 4096 KB - <braunr> ok - <braunr> manuel: performance should drop beyond bs=2M - <braunr> but that's not relevant anyway - <gnu_srs> Linux: bs=1M, 10.8 GB/s - <slpz> I think this difference is too big to be only due to a bigger amount - of CPU cycles... - <braunr> slpz: clearly - <slpz> gnu_srs: your host system has 64 or 32 bits? - <slpz> braunr: I'm going to investigate a bit - <slpz> but this accidental discovery just made my day. We're able to run - Hurd at decent speeds on newer hardware! - <braunr> slpz: what result do you get with the same test on your host - system ? - <manuel> interestingly, running it several times has made the performance - drop quite much (i'm getting 400-500MB/s with 1M now, compared to nearly - 800 fifteen minutes ago) - -[[Degradataion]]. - - <slpz> braunr: probably an almost infinite throughput, but I don't consider - that a valid test, since in Linux, the write operation to "/dev/null" - doesn't involve memory copying/moving - <braunr> manuel: i observed the same behaviour - <gnu_srs> slpz: Host system is 64 bit - <braunr> slpz: it doesn't on the hurd either - <braunr> slpz: (under 2k, that is) - <braunr> over* - <slpz> braunr: humm, you're right, as the null translator doesn't "touch" - the memory, CoW rules apply - <braunr> slpz: the only thing which actually copies things around is dd - <braunr> probably by simply calling read() - <braunr> which gets its result from a VM copy operation, but copies the - content to the caller provided buffer - <braunr> then vm_deallocate() the data from the storeio (zero) translator - <braunr> if storeio isn't too dumb, it doesn't even touch the transfered - buffer (as anonymous vm_map()ped memory is already cleared) - -[[!taglink open_issue_documentation]] - - <braunr> so this is a good test for measuring (profiling?) our ipc overhead - <braunr> and possibly the vm mapping operations (which could partly explain - why the results get worse over time) - <braunr> manuel: can you run vminfo | wc -l on your gnumach process ? - <slpz> braunr: Yes, unless some special situation apply, like the source - address/offset being unaligned, or if the translator decides to return - the result in a different buffer (which I assume is not the case for - storeio/zero) - <manuel> braunr: 35 - <braunr> slpz: they can't be unaligned, the vm code asserts that - <braunr> manuel: ok, this is normal - <slpz> braunr: address/offset from read() - <braunr> slpz: the caller provided buffer you mean ? - <slpz> braunr: yes, and the offset of the memory_object, if it's a pager - based translator - <braunr> slpz: highly unlikely, the compiler chooses appropriate alignments - for such buffers - <slpz> braunr: in those cases, memcpy is used over vm_copy - <braunr> slpz: and the glibc memcpy() optimized versions can usually deal - with that - <braunr> slpz: i don't get your point about memory objects - <braunr> slpz: requests on memory objects always have aligned values too - <slpz> braunr: sure, but can't deal with the user requesting non - page-aligned sizes - <braunr> slpz: we're considering our dd tests, for which we made sure sizes - were page aligned - <slpz> braunr: oh, I was talking in a general sense, not just in this dd - tests, sorry - <slpz> by the way, dd on the host tops at 12 GB/s with bs=2M - <braunr> that's consistent with our other results - <braunr> slpz: you mean, even on your i5 processor with 1.3 GiB/s on your - hurd kvm ? - <slpz> braunr: yes, on the GNU/Linux which is running as host - <braunr> slpz: well that's not consistent - <slpz> braunr: consistent with what? - <braunr> slpz: i get roughly the same result on my host, but ten times less - on my hurd kvm - <braunr> slpz: what's your kernel/kvm versions ? - <slpz> 2.6.32-5-amd64 (debian's build) 0.12.5 - <braunr> same here - <braunr> i'm a bit clueless - <braunr> why do i only get 130 MiB/s where you get 1.3 .. ? :) - <slpz> well, on my laptop, where Hurd on KVM tops on 50 MB/s, Linux gets a - bit more than 10 GB/s - <braunr> see - <braunr> slpz: reduce bs to 256k and test again if you have time please - <slpz> braunr: on which system? - <braunr> slpz: the fast one - <braunr> (linux host) - <slpz> braunr: Hurd? - <slpz> ok - <slpz> 12 GB/s - <braunr> i get 13.3 - <slpz> same for 128k, only at 64k starts dropping - <slpz> maybe, on linux we're being limited by memory speed, while on Hurd's - this test is (much) more CPU-bound? - <braunr> slpz: maybe - <braunr> too bad processor stalls aren't easy to measure - <slpz> braunr: that's very true. It's funny when you read a paper which - measures performance by cycles on an old RISC processor. That's almost - impossible to do (with reliability) nowadays :-/ - <slpz> I wonder which throughput can achieve Hurd running bare-metal on - this machine... - <antrik> both the Xeon and the i5 use cores based on the Nehalem - architecture - <antrik> apparently Nehalem is where Intel first introduces nested page - tables - <antrik> which pretty much explains the considerably lower overhead of VM - magic - <cjuner> antrik, what are nested page tables? (sounds like the 4-level page - tables we already have on amd64, or 2-level or 3-level on x86 pae) - <antrik> page tables were always 2-level on x86 - <antrik> that's unrelated - <antrik> nested page tables means there is another layer of address - translation, so the VMM can do it's own translation and doesn't care what - the guest system does => no longer has to intercept all page table - manipulations - <braunr> antrik: do you imply it only applies to virtualized systems ? - <antrik> braunr: yes - <slpz> antrik: Good guess. Looks like Intel's EPT are doing the trick by - allowing the guest OS deal with its own page faults - <slpz> antrik: next monday, I'll try disabling EPT support in KVM on that - machine (the fast one). That should confirm your theory empirically. - <slpz> this also means that there're too many page faults, as we should be - doing virtual copies of memory that is not being accessed - <slpz> and looking at how the value of "page faults" in "vmstat" increases, - shows that page faults are directly proportional to the number of pages - we are asking from the translator - <slpz> I've also tried doing a long read() directly, to be sure that "dd" - is not doing something weird, and it shows the same behaviour. - <braunr> slpz: dd does copy buffers - <braunr> slpz: i told you, it's not a good test case for pure virtual copy - evaluation - <braunr> antrik: do you know if xen benefits from nested page tables ? - <antrik> no idea - -[[!taglink open_issue_xen]] - - <slpz> braunr: but my small program doesn't, and still provokes a lot of - page faults - <braunr> slpz: are you certain it doesn't ? - <slpz> braunr: looking at google, it looks like recent Xen > 3.4 supports - EPT - <braunr> ok - <braunr> i'm ordering my new server right now, core i5 :) - <slpz> braunr: at least not explicitily. I need to look at MiG stubs again, - I don't remember if they do something weird. - <antrik> braunr: sandybridge or nehalem? :-) - <braunr> antrik: no idea - <antrik> does it tell a model number? - <braunr> not yet - <braunr> but i don't have a choice for that, so i'll order it first, check - after - <antrik> hehe - <antrik> I'm not sure it makes all that much difference anyways for a - server... unless you are running it at 100% load ;-) - <braunr> antrik: i'm planning on running xen guests suchs as new buildd - <antrik> hm... note though that some of the nehalem-generation i5s were - dual-core, while all the new ones are quad - <braunr> it's a quad - <antrik> the newer generation has better performance per GHz and per - Watt... but considering that we are rather I/O-limited in most cases, it - probably won't make much difference - <antrik> not sure whether there are further virtualisation improvements - that could be relevant... - <braunr> buildds spend much time running gcc, so even such improvements - should help - <braunr> there, server ordered :) - <braunr> antrik: model name : Intel(R) Core(TM) i5-2400 CPU @ 3.10GHz - -IRC, freenode, #hurd, 2011-09-06: - - <slpz> youpi: what machines are being used for buildd? Do you know if they - have EPT/RVI? - <youpi> we use PV Xen there - <slpz> I think Xen could also take advantage of those technologies. Not - sure if only in HVM or with PV too. - <youpi> only in HVM - <youpi> in PV it does not make sense: the guest already provides the - translated page table - <youpi> which is just faster than anything else - -IRC, freenode, #hurd, 2011-09-09: - - <antrik> oh BTW, for another data point: dd zero->null gets around 225 MB/s - on my lowly 1 GHz Pentium3, with a blocksize of 32k - <antrik> (but only half of that with 256k blocksize, and even less with 1M) - <antrik> the system has been up for a while... don't know whether it's - faster on a freshly booted one - -IRC, freenode, #hurd, 2011-09-15: - - <sudoman> - http://www.reddit.com/r/gnu/comments/k68mb/how_intelamd_inadvertently_fixed_gnu_hurd/ - <sudoman> so is the dd command pointed to by that article a measure of io - performance? - <antrik> sudoman: no, not really - <antrik> it's basically the baseline of what is possible -- but the actual - slowness we experience is more due to very unoptimal disk access patterns - <antrik> though using KVM with writeback caching does actually help with - that... - <antrik> also note that the title of this post really makes no - sense... nested page tables should provide similar improvements for *any* - guest system doing VM manipulation -- it's not Hurd-specific at all - <sudoman> ok, that makes sense. thanks :) - -IRC, freenode, #hurd, 2011-09-16: - - <slpz> antrik: I wrote that article (the one about How AMD/Intel fixed...) - <slpz> antrik: It's obviously a bit of an exaggeration, but it's true that - nested pages supposes a great improvement in the performance of Hurd - running on virtual machines - <slpz> antrik: and it's Hurd specific, as this system is more affected by - the cost of page faults - <slpz> antrik: and as the impact of virtualization on the performance is - much higher than (almost) any other OS. - <slpz> antrik: also, dd from /dev/zero to /dev/null it's a measure on how - fast OOL IPC is. |