iling
List; Peter Zijlstra; Steven Rostedt; Andrew Morton; Michel Lespinasse; Andi
Kleen; Rik van Riel; Paul E. McKenney; Raghavendra K T; George Spelvin; Tim
Chen; Chandramouleeswaran, Aswin; Norton, Scott J
Subject: Re: [PATCH v6 3/5] qrwlock: Enable fair queue read/write lock
On Tue, Nov 12, 2013
On Mon, Nov 18, 2013 at 10:46 AM, Andi Kleen wrote:
>> Why would it make sense here?
>
> There may be cases were switching all read locks to unfair may make
> concerete workloads slower.
Sorry, but I don't believe in "may be" as an excuse for complexity.
Especially since the "may be" faster perfo
> Why would it make sense here?
There may be cases were switching all read locks to unfair may make
concerete workloads slower.
The effect is very visible in (non kernel) lock micro benchmarks,
especially with HyperThreading.
With very high contention or long enough critical sections
the ordere
On Mon, Nov 18, 2013 at 10:34 AM, Andi Kleen wrote:
>
> FWIW unfair can be faster in some cases. It depends on the workload.
Sure. And we've never cared before.
When we switched over to the ticket spinlocks, we actually had
*numbers* about how the old unfair spinlocks could be faster. And we
sti
On Mon, Nov 18, 2013 at 10:11:48AM -0800, Linus Torvalds wrote:
> On Tue, Nov 12, 2013 at 6:48 AM, Waiman Long wrote:
> > By default, queue rwlock is fair among writers and gives preference
> > to readers allowing them to steal lock even if a writer is
> > waiting. However, there is a desire to ha
On Tue, Nov 12, 2013 at 6:48 AM, Waiman Long wrote:
> By default, queue rwlock is fair among writers and gives preference
> to readers allowing them to steal lock even if a writer is
> waiting. However, there is a desire to have a fair variant of
> rwlock that is more deterministic. To enable this
By default, queue rwlock is fair among writers and gives preference
to readers allowing them to steal lock even if a writer is
waiting. However, there is a desire to have a fair variant of
rwlock that is more deterministic. To enable this, fair variants
of lock initializers are added by this patch
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