linux-kernel - Re: [PATCH 0/2] block: Reinstate BLK_DEF_MAX

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Date:	Tue, 18 Aug 2015 13:22:03 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	Jeff Moyer <jmoyer@...hat.com>, hch@...radead.org
CC:	ed.cashin@....org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] block: Reinstate BLK_DEF_MAX_SECTORS

On 08/13/2015 11:57 AM, Jeff Moyer wrote:
> Commit 34b48db66e08 (block: remove artificial max_hw_sectors cap)
> caused performance regressions for streaming I/O workloads across
> a range of storage from SATA disks to enterprise storage arrays.
> I was unable to actually show a performance gain for any storage
> I have access to.  However, the patch was introduced to boost
> performance on software RAID over SATA disks, and I don't have
> access to such a configuration.
>
> The compromise is to reinstate BLK_DEF_MAX_SECTORS, but to bump it
> up to 2560 from 1024.  This number should allow full stripe writes
> to 10 data disks with a chunk size of 128KB, and at the same time
> does not regress the storage I have access to.
>
> [PATCH 1/2] Revert "block: remove artifical max_hw_sectors cap"
> [PATCH 2/2] block: bump BLK_DEF_MAX_SECTORS to 2560

Thanks, I added both. A bit annoying though, but better to fix up the 
perf regression now.

-- 
Jens Axboe

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