Re: [Bug 12309] Large I/O operations result in slow performanceand high iowait times

From: Thomas Pilarski
Date: Mon Nov 02 2009 - 15:28:06 EST

Hi Mike,

Am Montag, den 02.11.2009, 16:56 +0100 schrieb Mike Galbraith:
> > --- Comment #412 from Thomas Pilarski <thomas.pi@xxxxxxxx> 2009-11-01 21:28:24 ---
> > Created an attachment (id=23618)
> > --> (
> > Simple sleeper test case
> >
> > [...]
> Can you please try the latest -rc? I spent the day trying to coax a
> latency spike out of -tip, including thumping disk with dd, mysql+oltp
> rw test et al, and failed.

I have just tries the rc5 and the spikes are still there, but much
shorter. The test case does not show latencies <15ms. For these tests, I
have reduced the minimum printout time to 3ms. The notebook with the
first generation ssd in not available for testing, till next weekend.

The freezes still exists with the kernel 32, but the freezes are more
seldom and shorter. But I am not sure, as the X-Server is unusable on my
machine in vesa mode with the rc5 kernel.

Here are the results with the rc5 kernel and the fedora kernel
vmlinuz- I have changed my system yesterday.

This test was made during a kernel build.

Kernel 32:
Timediff 220114: 3.01ms Total: 9.44ms
Timediff 222460: 3.58ms Total: 10.82ms
Timediff 234968: 3.23ms Total: 9.99ms
Timediff 235916: 3.19ms Total: 11.50ms
Timediff 236448: 3.55ms Total: 12.71ms
Timediff 236485: 3.56ms Total: 16.14ms
Timediff 236793: 3.49ms Total: 10.54ms
Timediff 237076: 3.58ms Total: 11.29ms
Timediff 237417: 3.88ms Total: 12.05ms
Timediff 237694: 4.03ms Total: 15.36ms
Timediff 238039: 3.55ms Total: 11.64ms
Timediff 238347: 3.57ms Total: 10.23ms
Timediff 278945: 4.82ms Total: 11.25ms
Timediff 306303: 3.14ms Total: 10.22ms
Timediff 310378: 3.00ms Total: 9.49ms
Timediff 312685: 3.08ms Total: 9.53ms
Timediff 323824: 3.93ms Total: 10.37ms
Timediff 324150: 3.25ms Total: 9.90ms

With the kernel 31 the latencies are ~3-5ms with about 10 spikes every
10 seconds >15ms.

This test was made with eight concurrent writing operations. With kernel
32, the system freezes for up to 5 seconds. With the 31 kernel the
system is unusable and freezes for more than 15 seconds.

Kernel 32:
Timediff 541833: 5.45ms Total: 13.96ms
Timediff 541835: 5.96ms Total: 20.69ms
Timediff 562105: 47.17ms Total: 54.12ms
Timediff 562108: 4.72ms Total: 62.26ms
Timediff 562873: 3.51ms Total: 9.87ms
Timediff 562965: 4.80ms Total: 14.66ms
Timediff 563258: 5.82ms Total: 12.06ms
Timediff 564122: 4.54ms Total: 10.64ms
Timediff 564320: 4.41ms Total: 15.62ms
Timediff 565994: 3.52ms Total: 11.82ms
Timediff 571837: 4.84ms Total: 13.08ms
Timediff 574202: 6.26ms Total: 15.30ms
Timediff 580009: 4.26ms Total: 12.17ms
Timediff 581148: 5.97ms Total: 14.01ms
Timediff 604232: 8.06ms Total: 18.51ms
Timediff 607985: 36.17ms Total: 43.24ms
Timediff 607988: 6.44ms Total: 51.55ms
Timediff 607991: 3.96ms Total: 57.71ms
Timediff 608839: 3.15ms Total: 11.97ms
Timediff 621034: 11.70ms Total: 18.12ms
Timediff 626739: 14.79ms Total: 21.28ms
Timediff 628626: 4.29ms Total: 10.76ms
Timediff 630171: 3.17ms Total: 11.80ms
Timediff 630230: 4.68ms Total: 16.98ms
Timediff 645119: 5.24ms Total: 14.22ms
Timediff 645126: 3.01ms Total: 18.15ms
Timediff 665520: 23.39ms Total: 30.43ms
Timediff 665522: 7.21ms Total: 38.46ms
Timediff 665524: 4.05ms Total: 45.33ms
Timediff 665525: 12.37ms Total: 57.62ms
Timediff 665526: 8.55ms Total: 66.10ms
Timediff 666559: 7.40ms Total: 13.55ms
Timediff 666722: 9.98ms Total: 17.39ms
Timediff 692704: 3.91ms Total: 14.77ms
Timediff 709733: 5.22ms Total: 12.83ms
Timediff 713358: 9.96ms Total: 16.92ms
Timediff 713711: 6.71ms Total: 13.14ms
Timediff 713762: 9.60ms Total: 22.32ms
Timediff 715036: 6.61ms Total: 13.02ms
Timediff 715333: 8.16ms Total: 14.72ms
Timediff 716295: 5.69ms Total: 11.85ms
Timediff 717586: 13.30ms Total: 19.65ms
Timediff 720534: 4.00ms Total: 11.11ms
Timediff 724444: 3.78ms Total: 11.39ms
Timediff 742710: 5.91ms Total: 16.60ms
Timediff 746094: 9.36ms Total: 16.82ms
Timediff 746253: 3.01ms Total: 10.58ms
Timediff 750732: 3.12ms Total: 9.07ms
Timediff 750970: 4.66ms Total: 10.74ms
Timediff 751004: 11.48ms Total: 22.13ms
Timediff 751344: 3.24ms Total: 10.00ms
Timediff 752615: 6.09ms Total: 12.77ms
Timediff 752692: 10.48ms Total: 23.34ms
Timediff 752750: 5.66ms Total: 24.95ms
Timediff 753517: 5.40ms Total: 11.87ms
Timediff 764817: 3.01ms Total: 10.55ms
Timediff 780410: 7.68ms Total: 14.25ms
Timediff 781238: 3.22ms Total: 9.80ms
Timediff 781751: 4.32ms Total: 10.41ms
Timediff 783193: 3.02ms Total: 9.11ms
Timediff 783376: 5.04ms Total: 13.13ms
Timediff 783443: 10.43ms Total: 21.73ms
Timediff 783849: 3.56ms Total: 9.63ms
Timediff 783998: 4.75ms Total: 11.03ms
Timediff 789922: 14.12ms Total: 23.77ms
Timediff 791834: 10.17ms Total: 17.70ms
Timediff 791968: 4.33ms Total: 10.70ms
Timediff 803919: 8.23ms Total: 18.95ms
Timediff 814559: 22.20ms Total: 29.33ms
Timediff 814561: 8.97ms Total: 39.13ms
Timediff 814562: 9.33ms Total: 48.39ms
Timediff 814564: 3.54ms Total: 52.41ms
Timediff 814565: 11.44ms Total: 63.78ms
Timediff 814959: 6.00ms Total: 12.12ms
Timediff 816641: 7.36ms Total: 14.17ms
Timediff 817586: 8.70ms Total: 17.21ms
Timediff 817600: 3.01ms Total: 23.88ms
Timediff 818541: 11.60ms Total: 17.78ms
Timediff 836524: 9.60ms Total: 18.08ms
Timediff 847263: 7.33ms Total: 14.82ms
Timediff 847581: 3.92ms Total: 10.61ms
Timediff 857510: 5.21ms Total: 16.21ms
Timediff 875426: 34.63ms Total: 42.72ms
Timediff 875428: 15.56ms Total: 58.63ms
Timediff 875430: 4.25ms Total: 64.14ms
Timediff 875432: 9.90ms Total: 74.97ms

Kernel 31:
Timediff 3051355: 3.56ms Total: 12.01ms
Timediff 3052075: 3.04ms Total: 11.18ms
Timediff 3052727: 5.05ms Total: 11.98ms
Timediff 3052728: 6.32ms Total: 18.23ms
Timediff 3064913: 209.00ms Total: 215.89ms
Timediff 3087930: 7.33ms Total: 13.96ms
Timediff 3087931: 8.93ms Total: 22.84ms
Timediff 3088666: 10.73ms Total: 17.63ms
Timediff 3129442: 50.38ms Total: 57.85ms
Timediff 3129443: 6.97ms Total: 64.75ms
Timediff 3129444: 3.97ms Total: 68.64ms
Timediff 3129561: 9.71ms Total: 15.97ms
Timediff 3147899: 195.24ms Total: 202.19ms
Timediff 3202247: 4.25ms Total: 12.78ms
Timediff 3202480: 12.92ms Total: 19.53ms
Timediff 3202811: 8.06ms Total: 14.62ms
Timediff 3202812: 9.92ms Total: 24.48ms
Timediff 3207028: 10.27ms Total: 19.03ms
Timediff 3221487: 155.74ms Total: 162.68ms
Timediff 3245089: 16.85ms Total: 23.19ms
Timediff 3245090: 5.94ms Total: 29.07ms
Timediff 3245091: 8.93ms Total: 37.95ms
Timediff 3245092: 8.97ms Total: 46.85ms
Timediff 3283440: 33.92ms Total: 41.07ms

And this test during coping a file from one encrypted ext4 to a ext3
(data=ordered) partition.

Kernel 32:
Timediff 3519663: 4.30ms Total: 12.02ms
Timediff 3519949: 5.09ms Total: 15.30ms
Timediff 3520668: 4.49ms Total: 13.65ms
Timediff 3524199: 3.56ms Total: 12.34ms
Timediff 3525677: 4.10ms Total: 10.87ms
Timediff 3526071: 13.81ms Total: 21.45ms
Timediff 3526347: 11.53ms Total: 18.21ms
Timediff 3526606: 10.62ms Total: 17.31ms
Timediff 3526847: 9.90ms Total: 16.45ms
Timediff 3527074: 9.07ms Total: 15.46ms
Timediff 3529137: 5.50ms Total: 14.79ms
Timediff 3563927: 3.39ms Total: 13.19ms
Timediff 3622363: 3.96ms Total: 11.33ms
Timediff 3626268: 6.53ms Total: 14.77ms
Timediff 3626270: 5.92ms Total: 21.57ms
Timediff 3644582: 11.01ms Total: 21.53ms
Timediff 3654125: 8.69ms Total: 16.16ms
Timediff 3663323: 6.19ms Total: 12.83ms
Timediff 3663471: 5.55ms Total: 12.51ms
Timediff 3669593: 4.50ms Total: 11.63ms
Timediff 3679411: 4.84ms Total: 12.92ms
Timediff 3710494: 8.88ms Total: 18.84ms

Kernel 31:
Timediff 418897: 7.69ms Total: 32.66ms
Timediff 419046: 12.44ms Total: 21.66ms
Timediff 419048: 4.89ms Total: 26.98ms
Timediff 419788: 3.12ms Total: 13.01ms
Timediff 424485: 3.96ms Total: 12.58ms
Timediff 424492: 8.26ms Total: 20.69ms
Timediff 424909: 12.77ms Total: 22.17ms
Timediff 425081: 4.48ms Total: 23.68ms
Timediff 425362: 10.47ms Total: 19.98ms
Timediff 425365: 8.95ms Total: 28.83ms
Timediff 438326: 11.14ms Total: 21.51ms
Timediff 438534: 4.49ms Total: 24.64ms
Timediff 438817: 4.50ms Total: 26.54ms
Timediff 439276: 3.35ms Total: 10.78ms
Timediff 439278: 12.95ms Total: 23.66ms
Timediff 439717: 17.05ms Total: 26.49ms
Timediff 439937: 15.20ms Total: 22.50ms
Timediff 451047: 4.21ms Total: 12.41ms
Timediff 451454: 10.25ms Total: 19.86ms
Timediff 451606: 3.56ms Total: 23.22ms
Timediff 451984: 5.60ms Total: 18.60ms

The last test: dd if=/dev/zero of=test1 bs=1M count=8K to a ext3
(data=ordered) partition

Kernel 32: (Throughput 34,3 MB/s)
Timediff 3758684: 3.95ms Total: 14.74ms
Timediff 3761994: 3.53ms Total: 13.84ms
Timediff 3765917: 3.32ms Total: 14.68ms
Timediff 3770973: 3.63ms Total: 14.05ms
Timediff 3771301: 3.27ms Total: 13.44ms
Timediff 3774010: 3.02ms Total: 13.68ms
Timediff 3774263: 3.96ms Total: 14.41ms
Timediff 3777798: 4.01ms Total: 15.53ms
Timediff 3787290: 3.55ms Total: 14.39ms
Timediff 3787611: 3.60ms Total: 14.21ms
Timediff 3790433: 3.37ms Total: 14.14ms
Timediff 3790676: 3.09ms Total: 13.66ms
Timediff 3792464: 3.25ms Total: 13.16ms
Timediff 3792747: 3.34ms Total: 14.28ms
Timediff 3795961: 3.60ms Total: 13.72ms
Timediff 3797212: 4.00ms Total: 14.60ms
Timediff 3798908: 3.76ms Total: 14.49ms
Timediff 3803617: 4.48ms Total: 14.85ms
Timediff 3803855: 4.06ms Total: 14.67ms
Timediff 3805129: 3.71ms Total: 14.51ms
Timediff 3805431: 4.52ms Total: 15.55ms
Timediff 3807400: 4.17ms Total: 15.40ms
Timediff 3809013: 5.45ms Total: 16.39ms
Timediff 3811439: 3.51ms Total: 12.84ms
Timediff 3811680: 3.75ms Total: 14.83ms
Timediff 3823024: 4.02ms Total: 14.95ms
Timediff 3828474: 4.25ms Total: 14.74ms
Timediff 3836624: 3.03ms Total: 13.54ms
Timediff 3836919: 4.86ms Total: 16.72ms
Timediff 3845647: 3.74ms Total: 14.55ms
Timediff 3847453: 4.41ms Total: 15.06ms
Timediff 3847758: 3.12ms Total: 12.52ms
Timediff 3860736: 3.26ms Total: 14.12ms
Timediff 3860824: 5.95ms Total: 19.24ms
Timediff 3864060: 4.24ms Total: 14.29ms
Timediff 3866621: 4.02ms Total: 14.38ms
Timediff 3866863: 3.25ms Total: 13.00ms
Timediff 3871055: 4.54ms Total: 15.55ms
Timediff 3876891: 3.66ms Total: 15.05ms
Timediff 3883110: 4.13ms Total: 14.36ms
Timediff 3883432: 4.69ms Total: 15.04ms
Timediff 3890870: 4.31ms Total: 15.56ms
Timediff 3899279: 4.50ms Total: 15.60ms
Timediff 3906261: 3.82ms Total: 12.61ms
Timediff 3906605: 4.85ms Total: 15.35ms
Timediff 3908836: 4.27ms Total: 15.62ms
Timediff 3909079: 4.50ms Total: 15.37ms
Timediff 3910731: 3.57ms Total: 12.76ms
Timediff 3911044: 4.70ms Total: 14.80ms
Timediff 3912716: 4.67ms Total: 15.22ms
Timediff 3913027: 4.59ms Total: 15.39ms
Timediff 3914187: 4.00ms Total: 13.14ms
Timediff 3919700: 3.11ms Total: 14.77ms
Timediff 3921904: 4.76ms Total: 15.35ms
Timediff 3926853: 3.32ms Total: 14.19ms
Timediff 3926920: 4.03ms Total: 17.92ms
Timediff 3929504: 3.73ms Total: 14.70ms
Timediff 3929767: 4.13ms Total: 13.80ms
Timediff 3931576: 3.62ms Total: 14.70ms
Timediff 3931670: 3.04ms Total: 16.53ms
Timediff 3933039: 5.11ms Total: 16.19ms
Timediff 3935405: 3.83ms Total: 15.33ms
Timediff 3939429: 3.23ms Total: 14.50ms
Timediff 3940606: 4.34ms Total: 15.47ms
Timediff 3940825: 3.20ms Total: 15.06ms
Timediff 3950448: 3.14ms Total: 14.98ms
Timediff 3950727: 3.16ms Total: 14.17ms
Timediff 3968492: 3.16ms Total: 14.46ms

Kernel 31: (Throughput 33,7 MB/s)
Timediff 3759425: 8.49ms Total: 16.14ms
Timediff 3766033: 7.79ms Total: 15.44ms
Timediff 3786336: 10.13ms Total: 17.75ms
Timediff 3788547: 4.97ms Total: 12.63ms
Timediff 3790714: 4.80ms Total: 12.82ms
Timediff 3792863: 4.82ms Total: 12.52ms
Timediff 3795029: 5.45ms Total: 13.28ms
Timediff 3797198: 4.78ms Total: 13.02ms
Timediff 3797664: 109.83ms Total: 118.02ms
Timediff 3800212: 4.91ms Total: 13.50ms
Timediff 3806437: 5.78ms Total: 15.46ms
Timediff 3807558: 14.73ms Total: 23.01ms
Timediff 3808257: 16.44ms Total: 24.05ms
Timediff 3810303: 14.62ms Total: 23.92ms
Timediff 3812049: 18.96ms Total: 27.83ms
Timediff 3813914: 11.95ms Total: 20.75ms
Timediff 3814444: 4.79ms Total: 12.90ms
Timediff 3818132: 5.22ms Total: 14.41ms
Timediff 3831185: 5.02ms Total: 14.17ms
Timediff 3833362: 5.75ms Total: 13.66ms
Timediff 3845301: 8.16ms Total: 18.06ms

As you can see, the spikes are still there, but much more seldom and
shorter. Perhaps the opposite way, a delay or something equal in the
block-layer or scheduler to maximize this problem, can help to locate
the culprit.


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