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Date: Fri, 02 May 2014 10:56:16 -0600
From: Jens Axboe <axboe@kernel.dk>
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To: Christoph Hellwig <hch@infradead.org>
CC: Kent Overstreet <kmo@daterainc.com>, Ming Lei <tom.leiming@gmail.com>,
        Alexander Gordeev <agordeev@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Shaohua Li <shli@kernel.org>, Nicholas Bellinger <nab@linux-iscsi.org>,
        Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH RFC 0/2] percpu_ida: Take into account CPU topology when
 stealing tags
References: <CACVXFVN-roORYH8b-qZ10e2_wrL1W5-xO2P=A_ARPFL2GqDn2Q@mail.gmail.com> <535AD235.90604@kernel.dk> <CACVXFVPkiQT6yxse=sX1yuX8wLbr1sgbT4chQycbbPDR_A6hqA@mail.gmail.com> <535B13D7.4050202@kernel.dk> <CACVXFVORX_qgJNXcB3OFpscVx0eQAbLPv2Jr1N3_yBKrPsGXFA@mail.gmail.com> <53601602.5060306@kernel.dk> <20140501224744.GA2285@kmo-pixel> <536300BB.5060906@kernel.dk> <20140502050523.GA21708@infradead.org> <5363CAC4.4040306@kernel.dk> <20140502164305.GA18747@infradead.org>
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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