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

From: Waiman Long
Date: Wed Oct 11 2017 - 14:50:41 EST


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