From: Will Deacon <will@kernel.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-crypto@vger.kernel.org, herbert@gondor.apana.org.au,
linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com,
mark.rutland@arm.com, Dave Martin <dave.martin@arm.com>,
Eric Biggers <ebiggers@google.com>
Subject: Re: [PATCH 1/9] arm64: assembler: add cond_yield macro
Date: Thu, 28 Jan 2021 20:24:02 +0000 [thread overview]
Message-ID: <20210128202401.GD3016@willie-the-truck> (raw)
In-Reply-To: <20210128130625.54076-2-ardb@kernel.org>
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?
Will
next prev parent reply other threads:[~2021-01-28 20:25 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 [this message]
2021-01-28 20:25 ` Will Deacon
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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