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Message-Id: <1194920362.20251.161.camel@ymzhang> Date: Tue, 13 Nov 2007 10:19:22 +0800 From: "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com> To: Peter Zijlstra <a.p.zijlstra@...llo.nl> Cc: Benny Halevy <bhalevy@...asas.com>, LKML <linux-kernel@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, aneesh.kumar@...ux.vnet.ibm.com Subject: Re: iozone write 50% regression in kernel 2.6.24-rc1 On Mon, 2007-11-12 at 17:48 +0100, Peter Zijlstra wrote: > On Mon, 2007-11-12 at 17:05 +0200, Benny Halevy wrote: > > On Nov. 12, 2007, 15:26 +0200, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote: > > > Single socket, dual core opteron, 2GB memory > > > Single SATA disk, ext3 > > > > > > x86_64 kernel and userland > > > > > > (dirty_background_ratio, dirty_ratio) tunables > > > > > > ---- (5,10) - default > > > > > > 2.6.23.1-42.fc8 #1 SMP > > > > > > 524288 4 59580 60356 > > > 524288 4 59247 61101 > > > 524288 4 61030 62831 > > > > > > 2.6.24-rc2 #28 SMP PREEMPT > > > > > > 524288 4 49277 56582 > > > 524288 4 50728 61056 > > > 524288 4 52027 59758 > > > 524288 4 51520 62426 > > > > > > > > > ---- (20,40) - similar to your 8GB > > > > > > 2.6.23.1-42.fc8 #1 SMP > > > > > > 524288 4 225977 447461 > > > 524288 4 232595 496848 > > > 524288 4 220608 478076 > > > 524288 4 203080 445230 > > > > > > 2.6.24-rc2 #28 SMP PREEMPT > > > > > > 524288 4 54043 83585 > > > 524288 4 69949 516253 > > > 524288 4 72343 491416 > > > 524288 4 71775 492653 > > > > > > ---- (60,80) - overkill > > > > > > 2.6.23.1-42.fc8 #1 SMP > > > > > > 524288 4 208450 491892 > > > 524288 4 216262 481135 > > > 524288 4 221892 543608 > > > 524288 4 202209 574725 > > > 524288 4 231730 452482 > > > > > > 2.6.24-rc2 #28 SMP PREEMPT > > > > > > 524288 4 49091 86471 > > > 524288 4 65071 217566 > > > 524288 4 72238 492172 > > > 524288 4 71818 492433 > > > 524288 4 71327 493954 > > > > > > > > > While I see that the write speed as reported under .24 ~70MB/s is much > > > lower than the one reported under .23 ~200MB/s, I find it very hard to > > > believe my poor single SATA disk could actually do the 200MB/s for > > > longer than its cache 8/16 MB (not sure). > > > > > > vmstat shows that actual IO is done, even though the whole 512MB could > > > fit in cache, hence my suspicion that the ~70MB/s is the most realistic > > > of the two. > > > > Even 70 MB/s seems too high. What throughput do you see for the > > raw disk partition/ > > > > Also, are the numbers above for successive runs? > > It seems like you're seeing some caching effects so > > I'd recommend using a file larger than your cache size and > > the -e and -c options (to include fsync and close in timings) > > to try to eliminate them. > > ------ iozone -i 0 -r 4k -s 512m -e -c > > .23 (20,40) > > 524288 4 31750 33560 > 524288 4 29786 32114 > 524288 4 29115 31476 > > .24 (20,40) > > 524288 4 25022 32411 > 524288 4 25375 31662 > 524288 4 26407 33871 > > > ------ iozone -i 0 -r 4k -s 4g -e -c > > .23 (20,40) > > 4194304 4 39699 35550 > 4194304 4 40225 36099 > > > .24 (20,40) > > 4194304 4 39961 41656 > 4194304 4 39244 39673 > > > Yanmin, for that benchmark you ran, what was it meant to measure? > From what I can make of it its just write cache benching. Yeah. It's quite related to cache. I did more testing on my stoakley machine (8 cores, 8GB mem). If I reduce the memory to 4GB, the speed will be far slower. > > One thing I don't understand is how the write numbers are so much lower > than the rewrite numbers. The iozone code (which gives me headaches, > damn what a mess) seems to suggest that the only thing that is different > is the lack of block allocation. It might be a good direction. > > Linus posted a patch yesterday fixing up a regression in the ext3 bitmap > block allocator, /me goes apply that patch and rerun the tests. > > > > ---- (20,40) - similar to your 8GB > > > > > > 2.6.23.1-42.fc8 #1 SMP > > > > > > 524288 4 225977 447461 > > > 524288 4 232595 496848 > > > 524288 4 220608 478076 > > > 524288 4 203080 445230 > > > > > > 2.6.24-rc2 #28 SMP PREEMPT > > > > > > 524288 4 54043 83585 > > > 524288 4 69949 516253 > > > 524288 4 72343 491416 > > > 524288 4 71775 492653 > > 2.6.24-rc2 + > patches/wu-reiser.patch > patches/writeback-early.patch > patches/bdi-task-dirty.patch > patches/bdi-sysfs.patch > patches/sched-hrtick.patch > patches/sched-rt-entity.patch > patches/sched-watchdog.patch > patches/linus-ext3-blockalloc.patch > > 524288 4 179657 487676 > 524288 4 173989 465682 > 524288 4 175842 489800 > > > Linus' patch is the one that makes the difference here. So I'm unsure > how you bisected it down to: > > 04fbfdc14e5f48463820d6b9807daa5e9c92c51f Originally, my test suite is just to pick up the result of first run. Your prior patch(speed up writeback ramp-up on clean systems) fixed an issue about first run result regression. So my bisect captured it. However, late on, I found following run have different results. A moment ago, I retested 04fbfdc14e5f48463820d6b9807daa5e9c92c51f by: #git checkout 04fbfdc14e5f48463820d6b9807daa5e9c92c51f #make Then, reverse your patch. It looks like 04fbfdc14e5f48463820d6b9807daa5e9c92c51f is not the root cause of following run regression. I will change my test suite to make it run for many times and do a new bisect. > These results seem to point to > > 7c9e69faa28027913ee059c285a5ea8382e24b5d I tested 2.6.24-rc2 which already includes above patch. 2.6.24-rc2 has the same regression like 2.6.24-rc1. -yanmin - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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