Re: [PATCH] raid5:Only move IO_THRESHOLD stripes from delay_list to hold_list in raid5_activate_delayed().

[Dan Williams <dan.j.williams@xxxxxxxxx>]

On Fri, Jul 6, 2012 at 5:38 AM, majianpeng <majianpeng@xxxxxxxxx> wrote:
> To imporve write performance and as posssible as to achieve full-write,
> it only fetch IO_THRESHOLD stripes from delay_list to hold_list.
>
> Signed-off-by: majianpeng <majianpeng@xxxxxxxxx>

Yes, I do think we need something like this to further limit the
maximum in-flight pre-read, especially for the async / multithread xor
case where we process stripes faster.  However, this is the job of
get_priority_stripe(), not raid5_activate_delayed(), to rate limit
pre-reads versus full stripes.  One pre-read stripe at a time seems to
over bias full stripe writes.  I wonder if you see the same
performance effect by echo 0 >
/sys/block/<mddev>/md/preread_bypass_threshold?

--
Dan
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