Re: [linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch

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Subject: Re: [linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch
From: Lee Revell (rlrevell_AT_joe-job.com)
Date: Sat Jul 24 2004 - 08:46:01 EEST

On Sat, 2004-07-24 at 00:07, Lee Revell wrote:
> On Tue, 2004-07-20 at 08:19, Jens Axboe wrote:
> > On Tue, Jul 20 2004, Ingo Molnar wrote:
> > > > How much I/O do you allow to be in flight at once? It seems like by
> > > > decreasing the maximum size of I/O that you handle in one interrupt
> > > > you could improve this quite a bit. Disk throughput is good enough,
> > > > anyone in the real world who would feel a 10% hit would just throw
> > > > hardware at the problem.
> > >
> > it's not tweakable right now, but if you wish to experiment you just
> > need to add a line to ide-disk.c:idedisk_setup() - pseudo patch:
> >
> > + blk_queue_max_sectors(drive->queue, 32);
> > +
> I am currently testing the effect on throughput and will have some
> better numbers soon.

OK, here are my bonnie test results. They are not what I expected -
read and write performance is significantly better with 16KB max request
size, while seeking is much better with 1024KB.

jackd was running in the background in both cases. With 1024KB, there
were massive XRUNS, and worse, occasionally the soundcard interrupt was
completely lost for tens of milliseconds. This is what I would expect
if huge SG lists are being built in hardirq context. With 16KB, jackd
ran perfectly, the highest latency I was was about 100 usecs.

Kernel is 2.6.8-rc2 + voluntary-preempt-I4. CPU is 600Mhz, 512MB RAM.

16KB:

Version 1.03 ------Sequential Output------ --Sequential Input- --Random-
                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
mindpipe 1G 3002 88 31164 60 13485 29 3035 84 32838 36 56.7 0
                    ------Sequential Create------ --------Random Create--------
                    -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
                 16 94 40 +++++ +++ 15510 66 204 86 +++++ +++ 906 83
mindpipe,1G,3002,88,31164,60,13485,29,3035,84,32838,36,56.7,0,16,94,40,+++++,+++,15510,66,204,86,+++++,+++,906,83

1024KB:

Version 1.03 ------Sequential Output------ --Sequential Input- --Random-
                    -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
mindpipe 1G 2988 86 17647 29 10979 17 3114 90 28556 25 156.7 1
                    ------Sequential Create------ --------Random Create--------
                    -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
                 16 210 88 +++++ +++ 13295 62 215 89 +++++ +++ 920 84
mindpipe,1G,2988,86,17647,29,10979,17,3114,90,28556,25,156.7,1,16,210,88,+++++,+++,13295,62,215,89,+++++,+++,920,84

HD info:
/dev/hdc:

 Model=Maxtor 6Y160P0, FwRev=YAR41BW0, SerialNo=Y44K8TZE
 Config={ Fixed }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=57
 BuffType=DualPortCache, BuffSize=7936kB, MaxMultSect=16, MultSect=16
 CurCHS=4047/16/255, CurSects=16511760, LBA=yes, LBAsects=268435455
 IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes: pio0 pio1 pio2 pio3 pio4
 DMA modes: mdma0 mdma1 mdma2
 UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5 *udma6
 AdvancedPM=yes: disabled (255) WriteCache=enabled
 Drive conforms to: (null):

 * signifies the current active mode

Lee

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