Re: [PATCH v4 07/16] locking/rwsem: Implement lock handoff to prevent lock starvation
From: Waiman Long
Date: Tue Apr 16 2019 - 16:26:30 EST
On 04/16/2019 10:12 AM, Peter Zijlstra wrote:
> On Sat, Apr 13, 2019 at 01:22:50PM -0400, Waiman Long wrote:
>> + * The typical HZ value is either 250 or 1000. So set the minimum waiting
>> + * time to 4ms in the wait queue before initiating the handoff protocol.
>> + */
>> +#define RWSEM_WAIT_TIMEOUT (HZ/250)
> That seems equally unfortunate. For HZ=100 that results in 0ms, and for
> HZ=300 that results in 3 1/3-rd ms.
> (and this is not considering Alpha,ARM and MIPS, who all have various
> other 'creative' HZ values)
> In general aiming for sub 10ms timing using jiffies seems 'optimistic'.
I see your point. I will change it to use sched_clock() instead.