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From: "Reshetova, Elena" <elena.reshetova@intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: "'Peter Zijlstra'" <peterz@infradead.org>,
	"'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>,
	"'linux-fsdevel@vger.kernel.org'" <linux-fsdevel@vger.kernel.org>,
	"'gregkh@linuxfoundation.org'" <gregkh@linuxfoundation.org>,
	"'viro@zeniv.linux.org.uk'" <viro@zeniv.linux.org.uk>,
	"'tj@kernel.org'" <tj@kernel.org>,
	"'mingo@redhat.com'" <mingo@redhat.com>,
	"'hannes@cmpxchg.org'" <hannes@cmpxchg.org>,
	"'lizefan@huawei.com'" <lizefan@huawei.com>,
	"'acme@kernel.org'" <acme@kernel.org>,
	"'alexander.shishkin@linux.intel.com'" 
	<alexander.shishkin@linux.intel.com>,
	"'eparis@redhat.com'" <eparis@redhat.com>,
	"'akpm@linux-foundation.org'" <akpm@linux-foundation.org>,
	"'arnd@arndb.de'" <arnd@arndb.de>,
	"'luto@kernel.org'" <luto@kernel.org>,
	"'keescook@chromium.org'" <keescook@chromium.org>,
	"'dvhart@infradead.org'" <dvhart@infradead.org>,
	"'ebiederm@xmission.com'" <ebiederm@xmission.com>
Subject: RE: [PATCH 14/15] futex: convert futex_pi_state.refcount to refcount_t
Date: Mon, 23 Oct 2017 07:36:44 +0000	[thread overview]
Message-ID: <2236FBA76BA1254E88B949DDB74E612B802B428A@IRSMSX102.ger.corp.intel.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1710201424280.4531@nanos>


> On Fri, 20 Oct 2017, Reshetova, Elena wrote:
> 
> > Since I am not really sure what to do with this futex patch, I will drop it
> > from the new series that I am about to send now.
> >
> > Please let me know what exactly should I do with this patch, as I wrote
> > previously I really don't understand.
> 
> As Peter said:
> 
> > > > Now Thomas would like you to mention the fact that refcount_t doesn't
> > > > provide the exact same ordering as the atomic_t usages it replaces and
> > > > I think it would be good if you could hand-wave an argument on why the
> > > > futex code doesn't care.
> 
> So if you cannot come with a halfways reasonable argument then at least
> make it entirely clear that refcount_t is not the same as atomic_t in terms
> of ordering guarantees and you think that it does not matter but
> explicitely ask for help from the developers and maintainers to look at it.


There is another (I think better) proposal that came from Kees now: 
What if we change the default refcount_t to provide the strict memory
ordering like atomic_t?
I guess the reason why Peter intially went with *_relaxed() versions of compare and
exchange loop was performance. But now when we have x86 spec. fast
implementation, maybe it is ok to make the default FULL refcount slower?

What do people think of this?

Best Regards,
Elena.


> 
> Thanks,
> 
> 	tglx
> 

  reply	other threads:[~2017-10-23  7:37 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-30 12:22 [PATCH 00/15] v5 kernel core pieces refcount conversions Elena Reshetova
2017-08-30 12:22 ` [PATCH 01/15] sched: convert sighand_struct.count to refcount_t Elena Reshetova
2017-08-30 12:22 ` [PATCH 02/15] sched: convert signal_struct.sigcnt " Elena Reshetova
2017-08-30 12:22 ` [PATCH 03/15] sched: convert user_struct.__count " Elena Reshetova
2017-08-30 12:22 ` [PATCH 04/15] sched: convert numa_group.refcount " Elena Reshetova
2017-08-30 12:22 ` [PATCH 05/15] sched/task_struct: convert task_struct.usage " Elena Reshetova
2017-08-30 12:22 ` [PATCH 06/15] sched/task_struct: convert task_struct.stack_refcount " Elena Reshetova
2017-08-30 12:22 ` [PATCH 07/15] perf: convert perf_event_context.refcount " Elena Reshetova
2017-08-30 12:22 ` [PATCH 08/15] perf/ring_buffer: convert ring_buffer.refcount " Elena Reshetova
2017-08-30 12:22 ` [PATCH 09/15] perf/ring_buffer: convert ring_buffer.aux_refcount " Elena Reshetova
2017-08-30 12:22 ` [PATCH 10/15] uprobes: convert uprobe.ref " Elena Reshetova
2017-08-30 12:22 ` [PATCH 11/15] nsproxy: convert nsproxy.count " Elena Reshetova
2017-08-30 12:22 ` [PATCH 12/15] groups: convert group_info.usage " Elena Reshetova
2017-08-30 12:22 ` [PATCH 13/15] creds: convert cred.usage " Elena Reshetova
2017-08-30 12:22 ` [PATCH 14/15] futex: convert futex_pi_state.refcount " Elena Reshetova
2017-09-01  7:39   ` Thomas Gleixner
2017-09-01  9:38     ` Peter Zijlstra
2017-09-01  9:43       ` Thomas Gleixner
2017-09-01 10:52         ` Reshetova, Elena
2017-09-01 10:52           ` Reshetova, Elena
2017-09-01 11:05         ` Reshetova, Elena
2017-09-01 11:05           ` Reshetova, Elena
2017-09-01 12:34           ` Peter Zijlstra
2017-09-01 12:34             ` Peter Zijlstra
2017-09-01 13:24             ` Reshetova, Elena
2017-09-01 13:24               ` Reshetova, Elena
2017-09-01 13:36               ` Peter Zijlstra
2017-09-01 13:36                 ` Peter Zijlstra
2017-09-01 17:03                 ` Reshetova, Elena
2017-09-01 17:03                   ` Reshetova, Elena
2017-09-01 19:12                   ` Peter Zijlstra
2017-09-01 19:12                     ` Peter Zijlstra
2017-09-04 10:31                     ` Reshetova, Elena
2017-09-04 10:31                       ` Reshetova, Elena
2017-09-04 12:00                       ` Peter Zijlstra
2017-09-04 12:00                         ` Peter Zijlstra
2017-09-14 16:02                         ` Reshetova, Elena
2017-09-14 16:02                           ` Reshetova, Elena
2017-10-20 12:03                           ` Reshetova, Elena
2017-10-20 12:03                             ` Reshetova, Elena
2017-10-20 12:30                             ` Thomas Gleixner
2017-10-20 12:30                               ` Thomas Gleixner
2017-10-23  7:36                               ` Reshetova, Elena [this message]
2017-10-23  7:36                                 ` Reshetova, Elena
2017-08-30 12:22 ` [PATCH 15/15] kcov: convert kcov.refcount " Elena Reshetova
2017-08-31 23:48 ` [PATCH 00/15] v5 kernel core pieces refcount conversions Kees Cook
2017-09-01  9:48   ` Peter Zijlstra
2017-09-01 16:55     ` Kees Cook
2017-09-01 17:08       ` Reshetova, Elena
  -- strict thread matches above, loose matches on Subject: below --
2017-08-25  9:41 [PATCH 00/15] v4 " Elena Reshetova
2017-08-25  9:41 ` [PATCH 14/15] futex: convert futex_pi_state.refcount to refcount_t Elena Reshetova
2017-07-18 10:29 [PATCH 00/15] v4 kernel core pieces refcount conversions Elena Reshetova
2017-07-18 10:30 ` [PATCH 14/15] futex: convert futex_pi_state.refcount to refcount_t Elena Reshetova

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