From: Josh Triplett <josh@joshtriplett.org>
To: Ben Maurer <bmaurer@fb.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Paul Turner <pjt@google.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Andrew Hunter <ahh@google.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>
Subject: Re: [RFC PATCH] thread_local_abi system call: caching current CPU number (x86)
Date: Fri, 17 Jul 2015 10:03:00 -0700 [thread overview]
Message-ID: <20150717170300.GB1424@x> (raw)
In-Reply-To: <5CDDBDF2D36D9F43B9F5E99003F6A0D48D616ED9@PRN-MBX02-1.TheFacebook.com>
On Fri, Jul 17, 2015 at 10:49:19AM +0000, Ben Maurer wrote:
> Mathieu Desnoyers wrote:
> > Expose a new system call allowing threads to register a userspace memory
> > area where to store the current CPU number. Scheduler migration sets the
>
> I really like that this approach makes it easier to add a per-thread interaction between userspace and the kernel in the future.
>
> >+ if (!tlap || t->thread_local_abi_len <
> >+ offsetof(struct thread_local_abi, cpu)
> >+ + sizeof(tlap->cpu))
>
> Could you save a branch here by enforcing that thread_local_abi_len = 0 if thread_local_abi = null?
"saving a branch" doesn't seem like a good reason to do that; however,
it *is* the convention across other calls: if you pass 0, the pointer
is ignored, but if you pass non-zero, the pointer must be valid or you
get -EFAULT (or an actual segfault).
- Josh Triplett
next prev parent reply other threads:[~2015-07-17 17:03 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-16 20:00 [RFC PATCH] thread_local_abi system call: caching current CPU number (x86) Mathieu Desnoyers
[not found] ` <1437076851-14848-1-git-send-email-mathieu.desnoyers-vg+e7yoeK/dWk0Htik3J/w@public.gmane.org>
2015-07-17 10:49 ` Ben Maurer
2015-07-17 16:12 ` Mathieu Desnoyers
2015-07-17 17:03 ` Josh Triplett [this message]
2015-07-17 12:48 ` Nikolay Borisov
2015-07-17 16:23 ` Mathieu Desnoyers
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