linux-kernel - Re: [PATCH v6 00/11] locking/rwsem: Rework rwsem-xadd & enable new rwsem features

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Date:   Wed, 11 Oct 2017 14:50:34 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     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, Davidlohr Bueso <dave@...olabs.net>,
        Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH v6 00/11] locking/rwsem: Rework rwsem-xadd & enable new
 rwsem features

On 10/11/2017 02:48 PM, Peter Zijlstra wrote:
> On Wed, Oct 11, 2017 at 02:01:51PM -0400, Waiman Long wrote:
>>   # of Patches		   Reader 		  Writer
>>     Applied		Locking Rate		Locking Rate
>>   ------------		------------		------------
>> 	0	5,155/    5,155/    5,155    5,154/248,852/346,281
>> 	7	5,696/    5,697/    5,698  113,500/215,826/320,872
>> 	8	4,827/    5,047/    5,215    4,826/176,797/284,069
>> 	9     211,276/  509,712/1,134,007    4,894/221,839/246,818
>>        11     884,513/1,043,989/1,252,533    9,604/ 11,105/ 25,225
>>
>> It can be seen that rwsem changes from writer-preferring to
>> reader-preferring.
> A bit radically so, you almost starve the writers there.

Yes, almost, but the lock handoff code will make sure that it won't
actually get starved. That is why I added aggressive reader lock
stealing after the lock handoff code.

Cheers,
Longman