linux-kernel - Re: [PATCH 1/2] Convert target drivers to use sbitmap

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Date:   Tue, 15 May 2018 10:20:37 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Matthew Wilcox <willy@...radead.org>, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, target-devel@...r.kernel.org,
        linux1394-devel@...ts.sourceforge.net, linux-usb@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, Juergen Gross <jgross@...e.com>,
        qla2xxx-upstream@...gic.com,
        Kent Overstreet <kent.overstreet@...il.com>
Cc:     Matthew Wilcox <mawilcox@...rosoft.com>
Subject: Re: [PATCH 1/2] Convert target drivers to use sbitmap

On 5/15/18 10:11 AM, Jens Axboe wrote:
> On 5/15/18 10:00 AM, Matthew Wilcox wrote:
>> From: Matthew Wilcox <mawilcox@...rosoft.com>
>>
>> The sbitmap and the percpu_ida perform essentially the same task,
>> allocating tags for commands.  Since the sbitmap is more used than
>> the percpu_ida, convert the percpu_ida users to the sbitmap API.
> 
> It should also be the same performance as percpu_ida in light use, and
> performs much better at > 50% utilization of the tag space. I think
> that's better justification than "more used than".

Had to search long and hard for the perf numbers I did for percpu_ida
on higher utilization, but here it is:

https://lkml.org/lkml/2014/4/22/553

-- 
Jens Axboe