linux-kernel - Re: [PATCH] sata_sil: Greatly improve DMA support

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Message-ID: <4028.81.207.0.53.1179668330.squirrel@secure.samage.net>
Date:	Sun, 20 May 2007 15:38:50 +0200 (CEST)
From:	"Indan Zupancic" <indan@....nu>
To:	"Tejun Heo" <htejun@...il.com>
Cc:	"Jeff Garzik" <jeff@...zik.org>, linux-ide@...r.kernel.org,
	"LKML" <linux-kernel@...r.kernel.org>,
	"Alan Cox" <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] sata_sil: Greatly improve DMA support

On Sun, May 20, 2007 12:19, Tejun Heo wrote:
> Indan Zupancic wrote:
>> On Sun, May 20, 2007 00:03, Jeff Garzik wrote:
>>> Indan Zupancic wrote:
>>>> This patch seems to work with my SiI 3512, though I don't notice any
>>>> difference, neither a speedup, nor a slowdown. Hdparm gives the same
>>>> speeds (-tT), and cp -a'ing kernel sources is abysmal slow in both cases,
>>>> (need to look into that one) so I didn't really test it that well.
>>>
>>> It won't result in much of a speedup, except in situations where IOMMU
>>> or other situation that causes you to run into the 64k boundary being an
>>> issue -- generally only on huge transfers.
>>>
>>> A good measure is to dd(1) to/from the block device, rather than using a
>>> filesystem.  As has been shown on LKML, the filesystem can really slow
>>> things down in some cases.
>>
>> I didn't really expect a speedup, it's more that I've no regression to report.
>>
>> I could benchmark the patch more thoroughly, but right now I'm more worried
>> about the crawling cp I just discovered. Talking about filesystems slowing down
>> things...
>>
>> Test:
>>
>> $ cp -a linux-2.6/ /tmp/
>>
>> done on the same ext3 partition. linux-2.6 contains source and git repo only,
>> I'm compiling stuff with O=../obj.
>>
>> $ vmstat 10
>> procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
>>  r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
>>  0  1      0   4168   3316 195700    0    0   739   494  530  393 15  3 66 16
>>  0  3      4   4120   2040 198196    0    0 14677 14111 1247  435  0 17  0 83
>>  0  1      4   3588   1444 199696    0    0  8892  9472 1362  438  0 12  0 88
>>  1  0      4   3772   4228 196012    0    0   764   454 1161  345  0  4  0 96
>>  0  1      4   3548   6156 193088    0    0   793   851 1158  340  0  4  0 96
>>  0  1      4   3852   7608 189096    0    0   798   523 1160  474  1  4  0 95
>>  1  1      4   3612   8684 186048    0    0  1244   864 1178  430  2  5  0 93
>>  0  1      4  90660   9308  96396    0    0   853   906 1244  578  7  6  0 87
>>  0  1      4  72280   9816 112368    0    0   830   854 1278  429 12  5  0 83
>>  1  0      4  52488  10296 130560    0    0   935   861 1178  418  1  6  0 94
>>  0  1      4  30500  10788 149776    0    0   977   858 1178  371  0  6  0 94
>>  0  1      4   9792  11244 167856    0    0   918  1394 1182  350  1  5  0 94
>>  0  1      4   4016  11216 172504    0    0  1017   858 1181  382  1  6  0 94
>>  0  1      4   3660  11484 171484    0    0   966   861 1182  410  1  6  0 94
>>
>> It never finished, as I had no patience to copy about 900 Mb with this rate.
>>
>> As it's a git tree, I suppose it's heavily fragmented, but this is still rather
>> pathetic. Should I blame cp, or is something else wrong? Any ideas how
>> to figure this one out would be appreciated. Sorry for the off-topicness.
>
> Do things improve if you change the io scheduler to deadline?
>
>   # echo deadline > /sys/block/sda/queue/scheduler

I also tried noop, anticipatory, and now deadline, but it doesn't matter.

> Also worth looking at is the following bug entry.
>
>   http://bugzilla.kernel.org/show_bug.cgi?id=7372
>
> There seems to be weird interaction among the scheduler / VM / IO.  The
> exact cause is still not verified.  :-(

I know, I posted a bugreport too, but for starvation with the anticipatory scheduler.

Anyway, that bug seems unrelated to my case, as they have system unresponsiveness
or other nastiness, while I only have a crawling cp, which I blame on weaknesses
within ext3, a badly designed cp program and very fragmented filesystem. I just need
to verify that, somehow. I'll try with older kernels later.

Greetings,

Indan


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