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

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Date:	Fri, 2 May 2014 09:43:05 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Christoph Hellwig <hch@...radead.org>,
	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 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..

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