linux-kernel - Re: [RFC PATCH-tip 6/6] xfs: Enable reader optimistic spinning for DAX inodes

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Message-ID: <57605648.6060705@hpe.com>
Date:	Tue, 14 Jun 2016 15:08:56 -0400
From:	Waiman Long <waiman.long@....com>
To:	Christoph Hellwig <hch@...radead.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, <linux-kernel@...r.kernel.org>,
	<x86@...nel.org>, <linux-alpha@...r.kernel.org>,
	<linux-ia64@...r.kernel.org>, <linux-s390@...r.kernel.org>,
	<linux-arch@...r.kernel.org>, <xfs@....sgi.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Jason Low <jason.low2@...com>,
	Dave Chinner <david@...morbit.com>,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>
Subject: Re: [RFC PATCH-tip 6/6] xfs: Enable reader optimistic spinning for
 DAX inodes

On 06/14/2016 02:24 PM, Christoph Hellwig wrote:
> On Tue, Jun 14, 2016 at 02:12:39PM -0400, Waiman Long wrote:
>> This patch enables reader optimistic spinning for inodes that are
>> under a DAX-based mount point.
>>
>> On a 4-socket Haswell machine running on a 4.7-rc1 tip-based kernel,
>> the fio test with multithreaded randrw and randwrite tests on the
>> same file on a XFS partition on top of a NVDIMM with DAX were run,
>> the aggregated bandwidths before and after the patch were as follows:
> And why is this specific to DAX?  Many I/O operations already never
> got out to disk, and ilock is mostly held for operations that have
> nothing to do with disk I/O.

It is just a showcase for the rwsem change. We can certainly have more 
use cases.

Cheers,
Longman