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SubjectRe: [RFC] [PATCH] 2.5.35 patch for making DIO async
Date
> 
> On Wed, Sep 18, 2002 at 08:58:22AM -0700, Badari Pulavarty wrote:
> > Thanks for looking at the patch. Patch needed few cleanups to get it
> > working. Here is the status so far..
> >
> > 1) I tested synchronous raw read/write. They perform almost same as
> > without this patch. I am looking at why I can't match the performance.
> > (I get 380MB/sec on 40 dd's on 40 disks without this patch.
> > I get 350MB/sec with this patch).
>
> Hmm, we should try to improve that. Have you tried profiling a long run?


I took few shortcuts in the patch compared to original DIO code.
eg., I create a bio all the time.. original code reuses them.
But I don't think that is causing the performance hit. Anyway,
here is the vmstat and profile=2 output.

vmstat:

0 40 2 0 3804628 0 27396 0 0 344909 192 3786 3536 0 5 95
0 40 1 0 3803268 0 28628 0 0 345686 208 3793 3578 0 5 95
0 40 1 0 3802452 0 29404 0 0 346983 210 3806 3619 0 5 95
0 40 1 0 3801888 0 29932 0 0 345178 203 3786 3500 0 5 95
0 40 1 0 3801804 0 29996 0 0 345792 196 3791 3510 0 5 95
0 40 1 0 3801652 0 30100 0 0 346048 200 3800 3556 0 5 95

profile:

146796 default_idle 2293.6875
1834 __scsi_end_request 10.4205
1201 do_softirq 6.2552
891 scsi_dispatch_cmd 2.3203
50 __wake_up 1.0417
599 get_user_pages 0.7341
362 blk_rq_map_sg 0.6856
420 do_direct_IO 0.5707
25 dio_prep_bio 0.5208
562 __make_request 0.4878
55 __scsi_release_command 0.4167
6 cap_file_permission 0.3750
63 release_console_sem 0.3580
55 do_aic7xxx_isr 0.3438
141 bio_alloc 0.3389
45 scsi_finish_command 0.2557
8 scsi_sense_valid 0.2500
16 dio_new_bio 0.2500
206 schedule 0.2341

>
> > 2) wait_on_sync_kiocb() needed blk_run_queues() to make regular read/
> > write perform well.
>
> That should be somewhat conditional, but for now it sounds like the right
> thing to do.
>
> > 3) I am testing aio read/writes. I am using libaio.0.3.92.
> > When I try aio_read/aio_write on raw device, I am get OOPS.
> > Can I use libaio.0.3.92 on 2.5 ? Are there any interface
> > changes I need to worry between 2.4 and 2.5 ?
>
> libaio 0.3.92 should work on 2.5. Could you send me a copy of the
> decoded Oops?
>

My Bad :)

aio_read/aio_write() routines take loff_t not loff_t * (like regular read/writes)

ssize_t (*read) (struct file *, char *, size_t, loff_t *);
ssize_t (*aio_read) (struct kiocb *, char *, size_t, loff_t);

I coded for loff_t *. fixed it. I am testing it now.

Thanks,
Badari


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