From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: arcml <linux-snps-arc@lists.infradead.org>,
Alexey Brodkin <Alexey.Brodkin@synopsys.com>,
lkml <linux-kernel@vger.kernel.org>,
"Andy Lutomirski" <luto@amacapital.net>
Subject: Re: NMI for ARC
Date: Wed, 28 Sep 2016 10:58:06 -0700 [thread overview]
Message-ID: <3b5cbc7c-ed5c-af95-8dc9-25fd92277e98@synopsys.com> (raw)
In-Reply-To: <20160928071642.GU2794@worktop>
On 09/28/2016 12:16 AM, Peter Zijlstra wrote:
>> 1. Is it OK in general to short-circuit preemption off irq checks for NMI style
>> > interrupts.
> Yes. If the NMI returns to kernel space you must not attempt preemption
> for reasons you found :-), if the NMI returns to userspace you should do
> the normal return to user bits, I think.
Just to add, eliding preemption check in return path might not be sufficient as we
could still have timer intr leading to scheduler_tick() - whcih is what i found as
well ;-) So scheduler nevertheless needs to be told to not reschedule in this code
path.
So eliding preempt-off-irq just becomes an optimization for NMI code paths IMHO.
Now I was a stupid fool, fudging preemption counts in low level code, to achieve
this, whereas we have nice generic nmi_{enter,exit}() and in_nmi() helpers which
can be used.
Thx,
-Vineet
next prev parent reply other threads:[~2016-09-28 18:00 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1445286926.3913.13.camel@synopsys.com>
2015-11-17 9:14 ` local64_cmpxchg() in arc_perf_event_update() Vineet Gupta
2015-11-17 11:07 ` Peter Zijlstra
2015-11-17 11:23 ` Vineet Gupta
2015-11-17 12:24 ` Peter Zijlstra
2015-11-17 12:25 ` Peter Zijlstra
2015-11-17 12:53 ` NMI for ARC Vineet Gupta
2015-11-17 13:15 ` Peter Zijlstra
2016-09-28 0:22 ` Vineet Gupta
2016-09-28 7:16 ` Peter Zijlstra
2016-09-28 17:58 ` Vineet Gupta [this message]
2016-09-28 19:25 ` Andy Lutomirski
2016-09-28 20:37 ` Peter Zijlstra
2016-09-28 22:26 ` Andy Lutomirski
2016-09-28 22:44 ` Vineet Gupta
2016-09-28 22:47 ` Andy Lutomirski
2016-09-29 1:20 ` Vineet Gupta
2016-09-29 6:43 ` Peter Zijlstra
2016-09-29 16:47 ` Vineet Gupta
2016-09-29 18:54 ` Andy Lutomirski
2016-09-29 19:48 ` Vineet Gupta
2016-09-30 10:49 ` Peter Zijlstra
2016-09-29 17:30 ` Andy Lutomirski
2015-11-17 13:24 ` local64_cmpxchg() in arc_perf_event_update() Vineet Gupta
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