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Re: [PATCH 1/3] block: add blk-iopoll, a NAPI like approach for block devices

From:  Jens Axboe <jens.axboe-AT-oracle.com>
To:  Jeff Garzik <jeff-AT-garzik.org>
Subject:  Re: [PATCH 1/3] block: add blk-iopoll, a NAPI like approach for block devices
Date:  Fri, 7 Aug 2009 13:31:47 +0200
Cc:  Alan Cox <alan-AT-lxorguk.ukuu.org.uk>, linux-kernel-AT-vger.kernel.org, linux-scsi-AT-vger.kernel.org, Eric.Moore-AT-lsi.com
Archive-link:  Article, Thread

On Fri, Aug 07 2009, Jens Axboe wrote:
> On Fri, Aug 07 2009, Jens Axboe wrote:
> > > I'm not NAK'ing...  just inserting some relevant NAPI field experience,  
> > > and hoping for some numbers that better measure the costs/benefits.
> > 
> > Appreciate you looking over this, and I'll certainly be posting some
> > more numbers on this. It'll largely depend on both storage, controller,
> > and worload.
> 
> Here's a quick set of numbers, beating with random reads on a drive.
> Average of three runs for each, stddev is very low so confidence in the
> numbers should be high.
> 
> With iopoll=0 (disabled), stock:
> 
> blocksize       IOPS    ints/sec        usr     sys
> ------------------------------------------------------
> 4k              48401   ~30500          3.36%   27.26%
> 
> clat (usec): min=1052, max=21615, avg=10541.48, stdev=243.48
> clat (usec): min=1066, max=22040, avg=10543.69, stdev=242.05
> clat (usec): min=1057, max=23237, avg=10529.04, stdev=239.30
> 
> 
> With iopoll=1
> 
> blocksize       IOPS    ints/sec        usr     sys
> ------------------------------------------------------
> 4k              48452   ~29000          3.37%   26.47%
> 
> 
> clat (usec): min=1178, max=21662, avg=10542.72, stdev=247.87
> clat (usec): min=1074, max=21783, avg=10534.14, stdev=240.54
> clat (usec): min=1102, max=22123, avg=10509.42, stdev=225.73

Lets raise the bar a bit, this time using 8k reads on the faster box.

iopoll=0

blocksize       IOPS    ints/sec        usr     sys
------------------------------------------------------
8k              64050   ~76000          4.12%   45.01%

clat (usec): min=1326, max=18994, avg=7967.54, stdev=214.12
clat (usec): min=1325, max=25404, avg=7968.06, stdev=239.87
clat (usec): min=1273, max=21414, avg=7963.43, stdev=231.27


iopoll=1

blocksize       IOPS    ints/sec        usr     sys
------------------------------------------------------
8k              64162   ~55000          4.07%   42.32%

clat (usec): min=1380, max=19681, avg=7960.31, stdev=197.41
clat (usec): min=1370, max=37508, avg=7954.61, stdev=210.35
clat (usec): min=1332, max=23383, avg=7947.99, stdev=209.60

Again, purely a synthetic IO benchmark, but the sys reduction is
interesting.


-- 
Jens Axboe



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