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Date: Wed, 28 Jan 2009 15:04:38 -0800 From: Andrew Morton <akpm@...ux-foundation.org> To: Steven Patrick <steven@...s.net> Cc: bugme-daemon@...zilla.kernel.org, linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [Bugme-new] [Bug 12564] New: poor performance while preprocessing source code On Wed, 28 Jan 2009 14:43:37 -0800 Steven Patrick <steven@...s.net> wrote: > > > Problem Description: > > > Here's my situation. I've recently upgraded the kernels > > > on ~30 computers at work (from 2.6.21 to 2.6.27). These > > > computers are used to build and test software we develop. > > > We speed up the building process using distcc. However, > > > after the kernel upgrade, the builds are much much slower. > > > The preprocessing stage seems to be at least 10 times > > > slower. > > > As evidence of this slowdown I am attaching two images created > > > using distccmon-gnome. Both snapshots were taken shortly > > > after starting builds in a clean sandbox. The only difference > > > is the kernel. "fast.png" was generated while running > > > kernel 2.6.25.20. "slow.png" was generated with 2.6.26. > > > The light purple sections indicate the preprocessing times > > > for each file. > > > This slowdown is observed on both 32 and 64 bit computers > > > and using either gcc or the intel compiler. (The intel compiler > > > builds do not use distcc, but that are also slower.) Strangely > > > enough, it's still faster to use an NFS mounted sandbox on a > > > machine with an older kernel than the same sandbox on the local > > > machine with a newer kernel. (This suggests to me that it > > > is neither a disk or network IO problem.) > > > I've used git bisect to narrow it down to a single commit: > > > # bad: [b0b539739fe9b7d75002412a787cfdf4efddbc33] NFS: Ensure that 'noac' > > > and/or 'actimeo=0' turn off attribute caching > > > > And thanks for bisecting it. > > I think it might be possible to bisect further, but I > don't know how get git to do it. OK.. > > > This is the first commit after v2.6.26-rc3. I'm not an > > > experienced git user, so I don't know how to narrow it down > > > further. Distccmon-gnome snapshots from the bisection > > > process are similar to the ones noted above. > > > Naturally, I would like the newer kernels to have similar > > > performance to the older kernels. > > > I will be attaching various items. Let me know what other > > > information might be helpful. > > > > > > Steps to reproduce: > > > distccmon-gnome & > > > # using a makefile setup to use distcc: > > > make -j 5 all > > > # note preprocessing times in distccmon > > > > > > > Something I don't understand from this: > > > > If your normal setup is using distcc then what role does NFS have to > > play? I mean, distcc kind-of replaces NFS in this workload. > > I don't believe that this actually has anything to do > with NFS. The only way I could see NFS coming into this is the > fact that I use amd to automount home directories. > The commit mentioned above modifies just over 100 files, very > few of which appear related to NFS. I've attached the diifs. > It appears to be a number of fixes rolled up into one patch. > This is why I believe it might be possible to continue bisecting > with git. But, to do that I suspect I would need to use a > different repository and/or tag or version names. > BTW, the diffs were generated with "git diff v2.6.26-rc3" > after having done the bisection. This is why it looks to me > like this one commit includes multiple updates. Since all > bisection iterations were bad, the diffs against the good > version must be the diffs of the one commit. Of course, I > reserve the right to have made a mistake or not understand > things completely. > There was one other detail that seemed strange. In the > last four bisection iterations, the kernel identified > itself as -rc2 instead of -rc3. I assumed an update > accidentally changed it back. Heaven knows. OK, "This is the first commit after v2.6.26-rc3", so NFS is innocent. Presumably your git bisect landed on a big merge commit. I'm afaid I'm not the person who can tell you how to fix this - it hasn't happened to me in a while, but I don't know what I did to prevent it happening :( Here's the diffstat from your diffs.txt.gz: arch/m68k/configs/multi_defconfig | 1269 ------------------------- b/MAINTAINERS | 4 b/Makefile | 2 b/arch/arm/common/locomo.c | 66 - b/arch/arm/kernel/armksyms.c | 2 b/arch/arm/kernel/arthur.c | 2 b/arch/arm/mach-omap1/board-palmte.c | 2 b/arch/arm/mach-omap1/board-palmz71.c | 2 b/arch/arm/mach-omap2/board-2430sdp.c | 1 b/arch/arm/mach-omap2/board-apollon.c | 1 b/arch/arm/mach-omap2/board-generic.c | 1 b/arch/arm/mach-omap2/board-h4.c | 1 b/arch/arm/mach-omap2/clock.c | 4 b/arch/arm/mach-omap2/clock34xx.h | 21 b/arch/arm/mach-omap2/cm-regbits-34xx.h | 1 b/arch/arm/mach-omap2/mailbox.c | 25 b/arch/arm/mach-omap2/prm.h | 2 b/arch/arm/mach-orion5x/dns323-setup.c | 2 b/arch/arm/mach-orion5x/kurobox_pro-setup.c | 2 b/arch/arm/mach-pxa/colibri.c | 3 b/arch/arm/mach-pxa/spitz.c | 1 b/arch/arm/mm/proc-arm925.S | 2 b/arch/arm/mm/proc-arm926.S | 2 b/arch/arm/mm/proc-arm940.S | 2 b/arch/arm/mm/proc-arm946.S | 2 b/arch/arm/plat-omap/clock.c | 10 b/arch/arm/plat-omap/dma.c | 2 b/arch/arm/plat-omap/mailbox.c | 1 b/arch/blackfin/mach-bf527/boards/ezkit.c | 2 b/arch/m68k/Kconfig | 9 b/arch/m68k/configs/amiga_defconfig | 159 +-- b/arch/m68k/configs/apollo_defconfig | 140 -- b/arch/m68k/configs/atari_defconfig | 143 +- b/arch/m68k/configs/bvme6000_defconfig | 138 -- b/arch/m68k/configs/hp300_defconfig | 142 +- b/arch/m68k/configs/mac_defconfig | 144 +- b/arch/m68k/configs/mvme147_defconfig | 138 -- b/arch/m68k/configs/mvme16x_defconfig | 138 -- b/arch/m68k/configs/q40_defconfig | 159 +-- b/arch/m68k/configs/sun3_defconfig | 140 -- b/arch/m68k/configs/sun3x_defconfig | 140 -- b/arch/m68k/kernel/head.S | 2 b/arch/m68k/kernel/setup.c | 15 b/arch/powerpc/platforms/pasemi/misc.c | 7 b/arch/sparc64/defconfig | 40 b/arch/sparc64/mm/init.c | 2 b/arch/x86/kernel/process.c | 36 b/arch/x86/mm/pat.c | 2 b/drivers/block/amiflop.c | 6 b/drivers/block/z2ram.c | 2 b/drivers/char/snsc_event.c | 2 b/drivers/char/vme_scc.c | 4 b/drivers/i2c/busses/i2c-amd756.c | 2 b/drivers/i2c/busses/i2c-nforce2.c | 28 b/drivers/i2c/chips/max6875.c | 3 b/drivers/i2c/i2c-core.c | 22 b/drivers/ide/legacy/macide.c | 3 b/drivers/input/keyboard/hilkbd.c | 4 b/drivers/input/misc/hp_sdc_rtc.c | 5 b/drivers/input/serio/hp_sdc_mlc.c | 5 b/drivers/input/serio/q40kbd.c | 2 b/drivers/media/video/cs5345.c | 7 b/drivers/media/video/cs53l32a.c | 10 b/drivers/media/video/cx18/cx18-i2c.c | 9 b/drivers/media/video/cx25840/cx25840-core.c | 7 b/drivers/media/video/et61x251/et61x251_core.c | 2 b/drivers/media/video/ivtv/ivtv-i2c.c | 13 b/drivers/media/video/m52790.c | 9 b/drivers/media/video/msp3400-driver.c | 17 b/drivers/media/video/saa7115.c | 40 b/drivers/media/video/saa7127.c | 9 b/drivers/media/video/saa717x.c | 9 b/drivers/media/video/sn9c102/sn9c102_core.c | 2 b/drivers/media/video/tuner-core.c | 17 b/drivers/media/video/upd64031a.c | 6 b/drivers/media/video/upd64083.c | 6 b/drivers/media/video/vp27smpx.c | 9 b/drivers/media/video/wm8739.c | 7 b/drivers/media/video/wm8775.c | 7 b/drivers/media/video/zc0301/zc0301_core.c | 2 b/drivers/media/video/zoran_device.c | 2 b/drivers/media/video/zoran_driver.c | 2 b/drivers/net/82596.c | 7 b/drivers/net/apne.c | 3 b/drivers/net/mac89x0.c | 3 b/drivers/net/macmace.c | 3 b/drivers/net/sun3lance.c | 3 b/drivers/net/wireless/atmel.c | 2 b/drivers/video/Kconfig | 4 b/drivers/video/amifb.c | 4 b/drivers/video/dnfb.c | 3 b/drivers/video/hpfb.c | 2 b/drivers/video/pxafb.c | 5 b/fs/befs/endian.h | 2 b/fs/nfs/inode.c | 7 b/include/asm-arm/arch-omap/common.h | 4 b/include/asm-arm/arch-omap/control.h | 2 b/include/asm-arm/arch-omap/mmc.h | 24 b/include/asm-arm/arch-sa1100/irqs.h | 2 b/include/asm-arm/hardware/locomo.h | 19 b/include/asm-m68k/bug.h | 4 b/include/asm-m68k/io.h | 44 b/include/asm-m68k/setup.h | 2 b/include/asm-m68k/uaccess.h | 6 b/include/linux/i2c.h | 7 b/include/linux/i2c/pcf857x.h | 3 106 files changed, 833 insertions(+), 2743 deletions(-) Now, distcc has a long track record of tripping up bugs and regressions in the networking code - it's very clever that way. But it doesn't look like there were any relevant networking changes in that window. So I think the next step is to ask you to continue with (or redo) that bisection search. Is there someone who is more git-competent than I who could help with this please? -- 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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