From: Russell King - ARM Linux <linux@armlinux.org.uk>
To: Dave Martin <Dave.Martin@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Mark Rutland <mark.rutland@arm.com>,
linux-rt-users@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Will Deacon <will.deacon@arm.com>,
linux-kernel@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>,
tglx@linutronix.de, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH RT] arm*: disable NEON in kernel mode
Date: Fri, 1 Dec 2017 18:08:28 +0000 [thread overview]
Message-ID: <20171201180828.GN10595@n2100.armlinux.org.uk> (raw)
In-Reply-To: <20171201175844.GT22781@e103592.cambridge.arm.com>
On Fri, Dec 01, 2017 at 05:58:45PM +0000, Dave Martin wrote:
> +1, at least for arm64. I don't see a really compelling reason for
> holding kernel-mode NEON around memory management now that we have a
> strict save-once-restore-lazily model.
>
> This may not work so well for arm though -- I haven't looked at that
> code for a while.
>
>
> If there is memory manamement in any core loop, you already lost
> the performance battle, and an extra
> kernel_neon_end()+kernel_neon_begin() may not be that catastrophic.
Remember that we don't permit context switches while kernel neon is
in use on ARM - if there's any possibility of scheduling to occur,
the get_cpu() in kernel_neon_begin() should trigger a schedule-while-
atomic warning.
--
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 8.8Mbps down 630kbps up
According to speedtest.net: 8.21Mbps down 510kbps up
next prev parent reply other threads:[~2017-12-01 18:08 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-30 14:22 [PATCH RT] crypto: limit more FPU-enabled sections Sebastian Andrzej Siewior
2017-11-30 14:30 ` Sebastian Andrzej Siewior
2017-12-01 10:43 ` [PATCH RT] arm*: disable NEON in kernel mode Sebastian Andrzej Siewior
2017-12-01 13:45 ` Sebastian Andrzej Siewior
2017-12-01 14:18 ` Mark Rutland
2017-12-01 14:36 ` Sebastian Andrzej Siewior
2017-12-01 15:03 ` Ard Biesheuvel
2017-12-01 17:58 ` Dave Martin
2017-12-01 18:08 ` Russell King - ARM Linux [this message]
2017-12-01 18:24 ` Dave Martin
2017-12-01 19:20 ` Ard Biesheuvel
2017-12-04 9:21 ` Sebastian Andrzej Siewior
2017-12-01 17:14 ` Peter Zijlstra
2017-12-01 17:31 ` Russell King - ARM Linux
2017-12-01 17:39 ` Peter Zijlstra
2017-11-30 15:19 ` [PATCH RT] crypto: limit more FPU-enabled sections Steven Rostedt
2017-11-30 15:22 ` Sebastian Andrzej Siewior
2017-12-01 10:44 ` [PATCH RT v2] " Sebastian Andrzej Siewior
2017-12-01 11:32 ` Peter Zijlstra
2017-12-01 13:32 ` Sebastian Andrzej Siewior
2017-12-01 13:44 ` Peter Zijlstra
2017-12-01 13:50 ` Sebastian Andrzej Siewior
2017-12-01 14:03 ` [PATCH RT v3] " Sebastian Andrzej Siewior
2017-11-30 15:29 ` [PATCH RT] " Steven Rostedt
2017-11-30 15:41 ` Sebastian Andrzej Siewior
2017-11-30 16:18 ` Steven Rostedt
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