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Message-ID: <20190416141205.GK12232@hirez.programming.kicks-ass.net> Date: Tue, 16 Apr 2019 16:12:05 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Waiman Long <longman@...hat.com> Cc: Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>, Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org, x86@...nel.org, Davidlohr Bueso <dave@...olabs.net>, Linus Torvalds <torvalds@...ux-foundation.org>, Tim Chen <tim.c.chen@...ux.intel.com>, huang ying <huang.ying.caritas@...il.com> Subject: Re: [PATCH v4 07/16] locking/rwsem: Implement lock handoff to prevent lock starvation 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'.
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