On Friday December 22, Lars.Ellenberg@xxxxxxxxxx wrote:
>
> md raidX make_request functions strip off the BIO_RW_SYNC flag,
> this introducing additional latency.
>
> below is a suggested patch for the raid1.c .
> other suggested solutions would be to let the bio_clone do its work,
> and not reassign thereby stripping off all flags.
> at most strip off known unwanted flags (the BARRIER flag).
>
> similar pattern in the other raid versions.
Thanks. I think your patch is appropriate.
I don't like the idea of passing down any flags by default. If a flag
makes failure more likely (like BIO_RW_AHEAD or BIO_RW_FAILFAST) then
I *don't* want it passed down without making a conscious decision that
it is a good idea.
So yes, _SYNC should be passed down in raid1/raid10. More interesting
stuff would be needed in raid456.
_FAILFAST should probably never be passed down (well, maybe in
multipath, but who uses md/multipath??)
_META ... what is that ?? I'm not passing it down until I know!!
I'll look into this after the holidays. Meanwhile if you want to be
certain that this is in 2.6.20,
- Fix the retry-read case as well (where ->bi_rw is assigned about
10 lines from the end of raid1d()
- Create a 'perfect patch',
- add Acked-by: NeilBrown <neilb@xxxxxxx>
- and post it to akpm@xxxxxxxx (and appropriate lists).
Thanks,
NeilBrown
>
> cheers,
>
> Lars
>
>
> --- /mnt/kernel-src/linux-2.6.19/drivers/md/raid1.c.orig 2006-12-11 10:06:17.661776243 +0100
> +++ /mnt/kernel-src/linux-2.6.19/drivers/md/raid1.c 2006-12-12 11:09:55.975762364 +0100
> @@ -776,6 +776,7 @@ static int make_request(request_queue_t
> struct page **behind_pages = NULL;
> const int rw = bio_data_dir(bio);
> int do_barriers;
> + int do_sync = bio_sync(bio);
>
> /*
> * Register the new request and wait if the reconstruction
> @@ -835,7 +836,7 @@ static int make_request(request_queue_t
> read_bio->bi_sector = r1_bio->sector + mirror->rdev->data_offset;
> read_bio->bi_bdev = mirror->rdev->bdev;
> read_bio->bi_end_io = raid1_end_read_request;
> - read_bio->bi_rw = READ;
> + read_bio->bi_rw = READ | do_sync;
> read_bio->bi_private = r1_bio;
>
> generic_make_request(read_bio);
> @@ -906,7 +907,7 @@ static int make_request(request_queue_t
> mbio->bi_sector = r1_bio->sector + conf->mirrors[i].rdev->data_offset;
> mbio->bi_bdev = conf->mirrors[i].rdev->bdev;
> mbio->bi_end_io = raid1_end_write_request;
> - mbio->bi_rw = WRITE | do_barriers;
> + mbio->bi_rw = WRITE | do_barriers | do_sync;
> mbio->bi_private = r1_bio;
>
> if (behind_pages) {
>
>
> --
> : Lars Ellenberg Tel +43-1-8178292-55 :
> : LINBIT Information Technologies GmbH Fax +43-1-8178292-82 :
> : Vivenotgasse 48, A-1120 Vienna/Europe http://www.linbit.com :
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