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Subject: Re: [PATCH 1/2] Convert target drivers to use sbitmap
From:   Jens Axboe <axboe@kernel.dk>
To:     Matthew Wilcox <willy@infradead.org>, linux-kernel@vger.kernel.org,
        linux-scsi@vger.kernel.org, target-devel@vger.kernel.org,
        linux1394-devel@lists.sourceforge.net, linux-usb@vger.kernel.org,
        kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
        netdev@vger.kernel.org, Juergen Gross <jgross@suse.com>,
        qla2xxx-upstream@qlogic.com,
        Kent Overstreet <kent.overstreet@gmail.com>
Cc:     Matthew Wilcox <mawilcox@microsoft.com>
References: <20180515160043.27044-1-willy@infradead.org>
 <20180515160043.27044-2-willy@infradead.org>
 <3a56027b-47bc-dcb8-a465-3670031572f1@kernel.dk>
Message-ID: <6ab7d206-ba46-6b1e-5210-4894ec4dc553@kernel.dk>
Date:   Tue, 15 May 2018 10:20:37 -0600
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On 5/15/18 10:11 AM, Jens Axboe wrote:
> On 5/15/18 10:00 AM, Matthew Wilcox wrote:
>> From: Matthew Wilcox <mawilcox@microsoft.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