From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Dave Martin <Dave.Martin@arm.com>
Cc: Julien Grall <julien.grall@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-rt-users@vger.kernel.org, catalin.marinas@arm.com,
will.deacon@arm.com, ard.biesheuvel@linaro.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] arm64/fpsimd: Don't disable softirq when touching FPSIMD/SVE state
Date: Wed, 13 Feb 2019 17:50:34 +0100 [thread overview]
Message-ID: <20190213165034.mda5rdfwsxbcdtfa@linutronix.de> (raw)
In-Reply-To: <20190213153630.GK3567@e103592.cambridge.arm.com>
On 2019-02-13 15:36:30 [+0000], Dave Martin wrote:
> On Wed, Feb 13, 2019 at 03:30:29PM +0100, Sebastian Andrzej Siewior wrote:
> > On 2019-02-08 16:55:13 [+0000], Julien Grall wrote:
> > > When the kernel is compiled with CONFIG_KERNEL_MODE_NEON, some part of
> > > the kernel may be able to use FPSIMD/SVE. This is for instance the case
> > > for crypto code.
> > >
> > > Any use of FPSIMD/SVE in the kernel are clearly marked by using the
> > > function kernel_neon_{begin, end}. Furthermore, this can only be used
> > > when may_use_simd() returns true.
> >
> > This is equal what x86 is currently doing. The naming is slightly
> > different, there is irq_fpu_usable().
>
> Yes, I think it's basically the same idea.
>
> It's been evolving a bit on both sides, but is quite similar now.
I though that this is complicated and wanted to submit a patch to remove
irq_fpu_usable() and disable BH as part of kernel_fpu_begin() (but have
currently the onother FPU series ongoing which I want to finish first).
…
> "Usually" is probably not good enough if another task can run: if the
> preempting task enters userspace then the vector registers are needed
> for its use, which is tricky to arrange if the registers are currently
> in use by context switch logic running in the first task.
Yes.
> My current feeling is that we probably have to stick with
> preempt_disable() here, but hopefully we can get rid of
> local_bh_disable() (as proposed) with no ill effects...
>
> Does that sound sensible?
If you want to stick with may_use_simd() then yes.
> Cheers
> ---Dave
Sebastian
next prev parent reply other threads:[~2019-02-13 16:50 UTC|newest]
Thread overview: 29+ 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
2019-03-15 10:06 ` Dave Martin
2019-03-15 10:22 ` Julien Grall
2019-02-13 16:50 ` Sebastian Andrzej Siewior [this message]
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
2019-02-08 17:03 [PATCH 0/3] Remove reference of TIF_USEDFPU on arch not using it Julien Grall
2019-02-08 17:03 ` [RFC PATCH] arm64/fpsimd: Don't disable softirq when touching FPSIMD/SVE state Julien Grall
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