This may slow down sustained reads from softraid1 volume which consists of
drives w/ enabled read-ahead caches.
Just a guess, no tests performed.
2013/11/8 Ted Unangst <t...@tedunangst.com>
> This may be a bad idea. I can't really think of any pros or cons,
> other than a general principle of "when feasible, prefer random over
> deterministic".
>
>
>
> Index: softraid_raid1.c
> ===================================================================
> RCS file: /cvs/src/sys/dev/softraid_raid1.c,v
> retrieving revision 1.54
> diff -u -p -r1.54 softraid_raid1.c
> --- softraid_raid1.c 1 Nov 2013 17:36:19 -0000 1.54
> +++ softraid_raid1.c 7 Nov 2013 14:32:33 -0000
> @@ -350,8 +350,8 @@ sr_raid1_rw(struct sr_workunit *wu)
> rt = 0;
> ragain:
> /* interleave reads */
> - chunk = sd->mds.mdd_raid1.sr1_counter++ %
> - sd->sd_meta->ssdi.ssd_chunk_no;
> + chunk =
> +
> arc4random_uniform(sd->sd_meta->ssdi.ssd_chunk_no);
> scp = sd->sd_vol.sv_chunks[chunk];
> switch (scp->src_meta.scm_status) {
> case BIOC_SDONLINE:
> Index: softraidvar.h
> ===================================================================
> RCS file: /cvs/src/sys/dev/softraidvar.h,v
> retrieving revision 1.140
> diff -u -p -r1.140 softraidvar.h
> --- softraidvar.h 4 Nov 2013 21:02:57 -0000 1.140
> +++ softraidvar.h 7 Nov 2013 14:32:33 -0000
> @@ -417,7 +417,7 @@ struct sr_raid0 {
> /* RAID 1 */
> #define SR_RAID1_NOWU 16
> struct sr_raid1 {
> - u_int32_t sr1_counter;
> + u_int32_t sr1_unused;
> };
>
> /* RAID 4 */
>
>
