From: Will Deacon <will@kernel.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: mark.rutland@arm.com, herbert@gondor.apana.org.au,
Eric Biggers <ebiggers@google.com>,
catalin.marinas@arm.com, linux-crypto@vger.kernel.org,
Dave Martin <dave.martin@arm.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/9] arm64: assembler: add cond_yield macro
Date: Thu, 28 Jan 2021 20:25:09 +0000 [thread overview]
Message-ID: <20210128202509.GE3016@willie-the-truck> (raw)
In-Reply-To: <20210128202401.GD3016@willie-the-truck>
On Thu, Jan 28, 2021 at 08:24:01PM +0000, Will Deacon wrote:
> On Thu, Jan 28, 2021 at 02:06:17PM +0100, Ard Biesheuvel wrote:
> > Add a macro cond_yield that branches to a specified label when called if
> > the TIF_NEED_RESCHED flag is set and decreasing the preempt count would
> > make the task preemptible again, resulting in a schedule to occur. This
> > can be used by kernel mode SIMD code that keeps a lot of state in SIMD
> > registers, which would make chunking the input in order to perform the
> > cond_resched() check from C code disproportionately costly.
> >
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > ---
> > arch/arm64/include/asm/assembler.h | 16 ++++++++++++++++
> > 1 file changed, 16 insertions(+)
> >
> > diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
> > index bf125c591116..5f977a7c6b43 100644
> > --- a/arch/arm64/include/asm/assembler.h
> > +++ b/arch/arm64/include/asm/assembler.h
> > @@ -745,6 +745,22 @@ USER(\label, ic ivau, \tmp2) // invalidate I line PoU
> > .Lyield_out_\@ :
> > .endm
> >
> > + /*
> > + * Check whether preempt-disabled code should yield as soon as it
> > + * is able. This is the case if re-enabling preemption a single
> > + * time results in a preempt count of zero, and the TIF_NEED_RESCHED
> > + * flag is set. (Note that the latter is stored negated in the
> > + * top word of the thread_info::preempt_count field)
> > + */
> > + .macro cond_yield, lbl:req, tmp:req
> > +#ifdef CONFIG_PREEMPTION
> > + get_current_task \tmp
> > + ldr \tmp, [\tmp, #TSK_TI_PREEMPT]
> > + cmp \tmp, #PREEMPT_DISABLE_OFFSET
> > + beq \lbl
>
> Fancy that, I didn't know the '.' was optional in "b.eq"!
>
> Anyway, a very similar code sequence exists inside if_will_cond_yield_neon,
> only it doesn't touch the flags. Can we use that sequence instead, and then
> use the new macro from there?
... and now I noticed the last patch :)
But it would still be nice not to clobber the flags inside the macro.
Will
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next prev parent reply other threads:[~2021-01-28 20:26 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-28 13:06 [PATCH 0/9] arm64: rework NEON yielding to avoid scheduling from asm code Ard Biesheuvel
2021-01-28 13:06 ` [PATCH 1/9] arm64: assembler: add cond_yield macro Ard Biesheuvel
2021-01-28 20:24 ` Will Deacon
2021-01-28 20:25 ` Will Deacon [this message]
2021-01-28 20:26 ` Ard Biesheuvel
2021-01-28 13:06 ` [PATCH 2/9] crypto: arm64/sha1-ce - simplify NEON yield Ard Biesheuvel
2021-01-28 13:06 ` [PATCH 3/9] crypto: arm64/sha2-ce " Ard Biesheuvel
2021-01-28 13:06 ` [PATCH 4/9] crypto: arm64/sha3-ce " Ard Biesheuvel
2021-01-28 13:06 ` [PATCH 5/9] crypto: arm64/sha512-ce " Ard Biesheuvel
2021-01-28 13:06 ` [PATCH 6/9] crypto: arm64/aes-neonbs - remove NEON yield calls Ard Biesheuvel
2021-01-28 13:06 ` [PATCH 7/9] crypto: arm64/aes-ce-mac - simplify NEON yield Ard Biesheuvel
2021-01-28 13:06 ` [PATCH 8/9] crypto: arm64/crc-t10dif - move NEON yield to C code Ard Biesheuvel
2021-01-28 13:06 ` [PATCH 9/9] arm64: assembler: remove conditional NEON yield macros Ard Biesheuvel
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