From: Julien Grall <julien.grall@arm.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Dave Martin <Dave.Martin@arm.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
linux-rt-users@vger.kernel.org,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] arm64/fpsimd: Don't disable softirq when touching FPSIMD/SVE state
Date: Thu, 14 Mar 2019 18:07:19 +0000 [thread overview]
Message-ID: <abd861af-023f-2f9e-acee-4e1837aa8897@arm.com> (raw)
In-Reply-To: <20190304172535.v5pf7yboii7ayxnb@linutronix.de>
Hi Sebastian,
On 3/4/19 5:25 PM, Sebastian Andrzej Siewior wrote:
> On 2019-02-18 15:07:51 [+0000], Julien Grall wrote:
>> Hi,
> Hi,
>
>>> Wouldn't this arbitrarily increase softirq latency? Unconditionally
>>> forbidding SIMD in softirq might make more sense. It depends on how
>>> important the use cases are...
>
> It would increase the softirq latency but the question is how bad would
> it be. It would continue once the SIMD section is done.
On Arm, the kernel may use either FPSIMD or SVE (if supported by the
platform). While the FPSIMD context is fairly small (~4K), the SVE
context can be up to ~64KB.
> If you allow it but made it impossible to use (and use the software
> fallback) then it would slow down the processing. So…
This is a fair point. However, the use of crypto in softirqs seem to be
limited. So I am wondering whether disabling softirq in all the case is
worth it.
Would it be possible to consider to forbid/warn about using crypto in
softirqs?
>
>> Looking at the commit message from cb84d11e1625 "arm64: neon: Remove support
>> for nested or hardirq kernel-mode NEON", one of the use case for crypto in
>> softirq is certain mac80211 drivers.
>>
>> Is there any other use case for use crypto in softirqs?
>
> mac80211 does it for some wifi drivers. There used to be IPsec but I
> *think* this moved to the "parallel processing kthread".
I was able to find my way through mac80211 and confirm the use a taslket
and therefore softirqs. However, I got lost in the ipsec code.
> During my FPU rework on x86 I didn't find anything that does the
> processing in softirq (on my machine) so I hacked something so that I
> could test that I didn't break anything…
This is the same on the platform I have been using for testing.
Cheers,
--
Julien Grall
next prev parent reply other threads:[~2019-03-14 18:07 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-08 16:55 [RFC PATCH] arm64/fpsimd: Don't disable softirq when touching FPSIMD/SVE state Julien Grall
2019-02-12 17:13 ` Julia Cartwright
2019-02-18 14:07 ` Julien Grall
2019-02-13 14:30 ` Sebastian Andrzej Siewior
2019-02-13 15:36 ` Dave Martin
2019-02-13 15:40 ` Ard Biesheuvel
2019-02-13 15:42 ` Dave Martin
2019-02-13 16:52 ` Sebastian Andrzej Siewior
2019-02-14 10:34 ` Dave Martin
2019-02-18 15:07 ` Julien Grall
2019-03-04 17:25 ` Sebastian Andrzej Siewior
2019-03-14 18:07 ` Julien Grall [this message]
2019-03-15 10:06 ` Dave Martin
2019-03-15 10:22 ` Julien Grall
2019-02-13 16:50 ` Sebastian Andrzej Siewior
2019-02-18 14:33 ` Julien Grall
2019-02-18 16:32 ` Julien Grall
2019-04-04 10:52 ` Dave Martin
2019-04-05 9:02 ` Julien Grall
2019-04-05 14:39 ` Sebastian Andrzej Siewior
2019-04-05 15:17 ` Julien Grall
2019-04-05 15:42 ` Sebastian Andrzej Siewior
2019-04-11 15:12 ` Julien Grall
2019-04-05 15:07 ` Dave Martin
2019-04-11 15:58 ` Julien Grall
2019-04-11 16:34 ` Dave Martin
2019-04-11 16:50 ` Julien Grall
2019-04-11 14:10 ` Julien Grall
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