linux-kernel - Re: [PATCH RFC 0/2] percpu_ida: Take into account CPU topology when stealing tags

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Date:	Fri, 02 May 2014 10:56:16 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Christoph Hellwig <hch@...radead.org>
CC:	Kent Overstreet <kmo@...erainc.com>,
	Ming Lei <tom.leiming@...il.com>,
	Alexander Gordeev <agordeev@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Shaohua Li <shli@...nel.org>,
	Nicholas Bellinger <nab@...ux-iscsi.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH RFC 0/2] percpu_ida: Take into account CPU topology when
 stealing tags

On 05/02/2014 10:43 AM, Christoph Hellwig wrote:
> On Fri, May 02, 2014 at 10:41:40AM -0600, Jens Axboe wrote:
>>> At least for SCSI devices _tag space_ is plenty, it's just the we
>>> artifically limit our tag space to the queue depth to avoid having to
>>> track that one separately.  In addition we also preallocaste a request
>>> for each tag, so even if we would track the queue depth separately
>>> we would waste a lot of memory.
>>
>> In practice it comes out to the same, it's not feasible to run a much
>> larger space and track on queue depth. So I don't think that changes the
>> conclusion for SCSI.
> 
> Agreed.  Just had to check if my smart ass hat still fits this morning..

If not, these are on sale

http://www.cafepress.com/+smartass_trucker_hat,18823771

:-)

-- 
Jens Axboe

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