Messages in this thread | | | Date | Tue, 17 Mar 2015 10:55:33 -0700 | From | josh@joshtrip ... | Subject | Re: [RFC PATCH] sys_membarrier(): system/process-wide memory barrier (x86) (v12) |
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On Tue, Mar 17, 2015 at 04:36:27PM +0000, Mathieu Desnoyers wrote: > > > On Tue, Mar 17, 2015 at 01:45:25AM +0000, Mathieu Desnoyers wrote: > [...] > > > > > > > Would you see it as acceptable if we start by implementing > > > > only the non-expedited sys_membarrier() ? > > > > > > Sure. > > > > > > > Then we can add > > > > the expedited-private implementation after rq->curr becomes > > > > available through RCU. > > > > > > Yeah, or not at all; I'm still trying to get Paul to remove the > > > expedited nonsense from the kernel RCU bits; and now you want it in > > > userspace too :/ > > > > The non-expedited case makes sense when we batch RCU work > > with call_rcu. However, some users require to use synchronize_rcu() > > directly after modifying their data structure. Therefore, the > > latency associated with sys_membarrier() then becomes important, > > hence the interest for an expedited scheme. > > > > I agree that we should try to find a way to implement it with > > low disturbance on the CPU's rq locks. I'd be certainly > > OK with starting with just the non-expedited scheme, and add > > the expedited scheme later on. This is why we have the flags > > anyway. > > Paul, I'm currently reworking the patch to keep only the > non-expedited scheme. I don't need to touch the scheduler > internals anymore, so should I move the sys_membarrier > system call implementation into kernel/rcu/update.c ?
If you don't need access to scheduler internals, I'd suggest putting it in its own file (something like kernel/membarrier.c), so that you can use obj-$(CONFIG_MEMBARRIER) in a Makefile to enable/disable it rather than an #ifdef in a .c file.
- Josh Triplett
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