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Date: Mon, 4 Sep 2017 10:31:54 +0000 From: "Reshetova, Elena" <elena.reshetova@...el.com> To: Peter Zijlstra <peterz@...radead.org> CC: Thomas Gleixner <tglx@...utronix.de>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>, "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>, "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>, "tj@...nel.org" <tj@...nel.org>, "mingo@...hat.com" <mingo@...hat.com>, "hannes@...xchg.org" <hannes@...xchg.org>, "lizefan@...wei.com" <lizefan@...wei.com>, "acme@...nel.org" <acme@...nel.org>, "alexander.shishkin@...ux.intel.com" <alexander.shishkin@...ux.intel.com>, "eparis@...hat.com" <eparis@...hat.com>, "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>, "arnd@...db.de" <arnd@...db.de>, "luto@...nel.org" <luto@...nel.org>, "keescook@...omium.org" <keescook@...omium.org>, "dvhart@...radead.org" <dvhart@...radead.org>, "ebiederm@...ssion.com" <ebiederm@...ssion.com> Subject: RE: [PATCH 14/15] futex: convert futex_pi_state.refcount to refcount_t > -----Original Message----- > From: Peter Zijlstra [mailto:peterz@...radead.org] > Sent: Friday, September 1, 2017 10:13 PM > To: Reshetova, Elena <elena.reshetova@...el.com> > Cc: Thomas Gleixner <tglx@...utronix.de>; linux-kernel@...r.kernel.org; linux- > fsdevel@...r.kernel.org; gregkh@...uxfoundation.org; viro@...iv.linux.org.uk; > tj@...nel.org; mingo@...hat.com; hannes@...xchg.org; lizefan@...wei.com; > acme@...nel.org; alexander.shishkin@...ux.intel.com; eparis@...hat.com; > akpm@...ux-foundation.org; arnd@...db.de; luto@...nel.org; > keescook@...omium.org; dvhart@...radead.org; ebiederm@...ssion.com > Subject: Re: [PATCH 14/15] futex: convert futex_pi_state.refcount to refcount_t > > On Fri, Sep 01, 2017 at 05:03:55PM +0000, Reshetova, Elena wrote: > > > On Fri, Sep 01, 2017 at 01:24:16PM +0000, Reshetova, Elena wrote: > > > > > > > > > On Fri, Sep 01, 2017 at 11:05:33AM +0000, Reshetova, Elena wrote: > > > > > > Actually on the second thought: does the above memory ordering > differences > > > > > > really apply when we have ARCH_HAS_REFCOUNT? To me it looks like the > way > > > > > > how it is currently implemented for x86 is the same way as it is for atomic > > > cases. > > > > > > > > > > Never look to x86 for memory ordering, its boring. > > > > > > > > > > And yes, for the ARM implementation it can certainly make a difference. > > > > > > > > So, yes, what I am trying to say is that it can really depend if you have > > > ARCH_HAS_REFCOUNT > > > > enabled or not and then also based on architecture. Thus I believe is also true > for > > > atomic: there > > > > might be differences when you use arch. dependent version of function or not. > > > > > > So the generic one in lib/refcount.c is already weaker on ARM, they > > > don't need to do a ARCH specific 'fast' implementation for the > > > difference to show up. > > > > But can they make "fast" implementation on ARM that would give stronger > memory guarantees? > > Whatever for? Well, maybe just by default when arch.-specific implementation is done. But I was just trying to speculate to understand. I will resend this one with new comment added. Still not sure if I need to resend the whole series with updated commits or break this up by individual patches further for the separate merges.
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