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Message-ID: <87ha3qcp6y.fsf@vitty.brq.redhat.com> Date: Thu, 12 Jun 2014 14:00:53 +0200 From: Vitaly Kuznetsov <vkuznets@...hat.com> To: Roger Pau Monné <roger.pau@...rix.com> Cc: <xen-devel@...ts.xenproject.org>, <axboe@...nel.dk>, <felipe.franciosi@...rix.com>, Greg KH <gregkh@...uxfoundation.org>, <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>, <jerry.snitselaar@...cle.com>, Jiri Slaby <jslaby@...e.cz>, Ronen Hod <rhod@...hat.com>, Andrew Jones <drjones@...hat.com> Subject: Re: [Xen-devel] Backport request to stable of two performance related fixes for xen-blkfront (3.13 fixes to earlier trees) Roger Pau Monné <roger.pau@...rix.com> writes: > On 10/06/14 15:19, Vitaly Kuznetsov wrote: >> Vitaly Kuznetsov <vkuznets@...hat.com> writes: >> >>> Jiri Slaby <jslaby@...e.cz> writes: >>> >>>> On 06/04/2014 07:48 AM, Greg KH wrote: >>>>> On Wed, May 14, 2014 at 03:11:22PM -0400, Konrad Rzeszutek Wilk wrote: >>>>>> Hey Greg >>>>>> >>>>>> This email is in regards to backporting two patches to stable that >>>>>> fall under the 'performance' rule: >>>>>> >>>>>> bfe11d6de1c416cea4f3f0f35f864162063ce3fa >>>>>> fbe363c476afe8ec992d3baf682670a4bd1b6ce6 >>>>> >>>>> Now queued up, thanks. >>>> >>>> AFAIU, they introduce a performance regression. >>>> >>>> Vitaly? >>> >>> I'm aware of a performance regression in a 'very special' case when >>> ramdisks or files on tmpfs are being used as storage, I post my results >>> a while ago: >>> https://lkml.org/lkml/2014/5/22/164 >>> I'm not sure if that 'special' case requires investigation and/or should >>> prevent us from doing stable backport but it would be nice if someone >>> tries to reproduce it at least. >>> >>> I'm going to make a bunch of tests with FusionIO drives and sequential >>> read to replicate same test Felipe did, I'll report as soon as I have >>> data (beginning of next week hopefuly). >> >> Turns out the regression I'm observing with these patches is not >> restricted to tmpfs/ramdisk usage. >> >> I was doing tests with Fusion-io ioDrive Duo 320GB (Dual Adapter) on HP >> ProLiant DL380 G6 (2xE5540, 8G RAM). Hyperthreading is disabled, Dom0 is >> pinned to CPU0 (cores 0,1,2,3) I run up to 8 guests with 1 vCPU each, >> they are pinned to CPU1 (cores 4,5,6,7,4,5,6,7). I tried differed >> pinning (Dom0 to 0,1,4,5, DomUs to 2,3,6,7,2,3,6,7 to balance NUMA, that >> doesn't make any difference to the results). I was testing on top of >> Xen-4.3.2. >> >> I was testing two storage configurations: >> 1) Plain 10G partitions from one Fusion drive (/dev/fioa) are attached >> to guests >> 2) LVM group is created on top of both drives (/dev/fioa, /dev/fiob), >> 10G logical volumes are created with striping (lvcreate -i2 ...) >> >> Test is done by simultaneous fio run in guests (rw=read, direct=1) for >> 10 second. Each test was performed 3 times and the average was taken. >> Kernels I compare are: >> 1) v3.15-rc5-157-g60b5f90 unmodified >> 2) v3.15-rc5-157-g60b5f90 with 427bfe07e6744c058ce6fc4aa187cda96b635539, >> bfe11d6de1c416cea4f3f0f35f864162063ce3fa, and >> fbe363c476afe8ec992d3baf682670a4bd1b6ce6 reverted. >> >> First test was done with Dom0 with persistent grant support (Fedora's >> 3.14.4-200.fc20.x86_64): >> 1) Partitions: >> http://hadoop.ru/pubfiles/bug1096909/fusion/315_pgrants_partitions.png >> (same markers mean same bs, we get 860 MB/s here, patches make no >> difference, result matches expectation) >> >> 2) LVM Stripe: >> http://hadoop.ru/pubfiles/bug1096909/fusion/315_pgrants_stripe.png >> (1715 MB/s, patches make no difference, result matches expectation) >> >> Second test was performed with Dom0 without persistent grants support >> (Fedora's 3.7.9-205.fc18.x86_64) >> 1) Partitions: >> http://hadoop.ru/pubfiles/bug1096909/fusion/315_nopgrants_partitions.png >> (860 MB/sec again, patches worsen a bit overall throughput with 1-3 >> clients) >> >> 2) LVM Stripe: >> http://hadoop.ru/pubfiles/bug1096909/fusion/315_nopgrants_stripe.png >> (Here we see the same regression I observed with ramdisks and tmpfs >> files, unmodified kernel: 1550MB/s, with patches reverted: 1715MB/s). >> >> The only major difference with Felipe's test is that he was using >> blktap3 with XenServer and I'm using standard blktap2. > > Hello, > > I don't think you are using blktap2, I guess you are using blkback. Right, sorry for the confusion. > Also, running the test only for 10s and 3 repetitions seems too low, I > would probably try to run the tests for a longer time and do more > repetitions, and include the standard deviation also. > > Could you try to revert the patches independently to see if it's a > specific commit that introduces the regression? I did additional test runs. Now I'm comparing 3 kernels: 1) Unmodified v3.15-rc5-157-g60b5f90 - green color on chart 2) v3.15-rc5-157-g60b5f90 with bfe11d6de1c416cea4f3f0f35f864162063ce3fa and 427bfe07e6744c058ce6fc4aa187cda96b635539 reverted (so only fbe363c476afe8ec992d3baf682670a4bd1b6ce6 "xen-blkfront: revoke foreign access for grants not mapped by the backend" left) - blue color on chart 3) v3.15-rc5-157-g60b5f90 with all (bfe11d6de1c416cea4f3f0f35f864162063ce3fa, 427bfe07e6744c058ce6fc4aa187cda96b635539, fbe363c476afe8ec992d3baf682670a4bd1b6ce6) patches reverted - red color on chart. I test on top of striped LVM on 2 FusionIO drives, I do 3 repetitions for 30 seconds each. The result is here: http://hadoop.ru/pubfiles/bug1096909/fusion/315_nopgrants_20140612.png It is consistent with what I've measured with ramdrives and tmpfs files: 1) fbe363c476afe8ec992d3baf682670a4bd1b6ce6 "xen-blkfront: revoke foreign access for grants not mapped by the backend" brings us the regression. Bigger block size is - bigger the difference but the regression is observed with all block sizes > 8k. 2) bfe11d6de1c416cea4f3f0f35f864162063ce3fa "xen-blkfront: restore the non-persistent data path" brings us performance improvement but with conjunction with fbe363c476afe8ec992d3baf682670a4bd1b6ce6 it is still worse than the kernel without both patches. My Dom0 is Fedora's 3.7.9-205.fc18.x86_64. I can test on newer blkback, however I'm not aware of any way to disable persistent grants there (there is no regression when they're used). > > Thanks, Roger. Thanks, -- Vitaly -- 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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