From: Dave Martin <Dave.Martin@arm•com>
To: Mark Brown <broonie@kernel•org>
Cc: Julien Grall <julien@xen•org>,
Catalin Marinas <catalin.marinas@arm•com>,
zhang.lei@jp•fujitsu.com, Julien Grall <julien.grall@arm•com>,
Will Deacon <will@kernel•org>,
linux-arm-kernel@lists•infradead.org,
Daniel Kiss <Daniel.Kiss@arm•com>
Subject: Re: [PATCH v3 5/8] arm64/sve: Implement a helper to flush SVE registers
Date: Wed, 15 Jul 2020 17:52:05 +0100 [thread overview]
Message-ID: <20200715165205.GD30452@arm.com> (raw)
In-Reply-To: <20200629133556.39825-6-broonie@kernel.org>
On Mon, Jun 29, 2020 at 02:35:53PM +0100, Mark Brown wrote:
> From: Julien Grall <julien.grall@arm•com>
>
> Introduce a new helper that will zero all SVE registers but the first
> 128-bits of each vector. This will be used by subsequent patches to
> avoid costly store/maipulate/reload sequences in places like do_sve_acc().
>
> Signed-off-by: Julien Grall <julien.grall@arm•com>
> Reviewed-by: Dave Martin <Dave.Martin@arm•com>
> Signed-off-by: Mark Brown <broonie@kernel•org>
> ---
> arch/arm64/include/asm/fpsimd.h | 1 +
> arch/arm64/include/asm/fpsimdmacros.h | 19 +++++++++++++++++++
> arch/arm64/kernel/entry-fpsimd.S | 8 ++++++++
> 3 files changed, 28 insertions(+)
>
> diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h
> index 59f10dd13f12..958f642e930d 100644
> --- a/arch/arm64/include/asm/fpsimd.h
> +++ b/arch/arm64/include/asm/fpsimd.h
> @@ -69,6 +69,7 @@ static inline void *sve_pffr(struct thread_struct *thread)
> extern void sve_save_state(void *state, u32 *pfpsr);
> extern void sve_load_state(void const *state, u32 const *pfpsr,
> unsigned long vq_minus_1);
> +extern void sve_flush_live(void);
> extern unsigned int sve_get_vl(void);
>
> struct arm64_cpu_capabilities;
> diff --git a/arch/arm64/include/asm/fpsimdmacros.h b/arch/arm64/include/asm/fpsimdmacros.h
> index feef5b371fba..af43367534c7 100644
> --- a/arch/arm64/include/asm/fpsimdmacros.h
> +++ b/arch/arm64/include/asm/fpsimdmacros.h
> @@ -164,6 +164,13 @@
> | ((\np) << 5)
> .endm
>
> +/* PFALSE P\np.B */
> +.macro _sve_pfalse np
> + _sve_check_preg \np
> + .inst 0x2518e400 \
> + | (\np)
> +.endm
> +
> .macro __for from:req, to:req
> .if (\from) == (\to)
> _for__body %\from
> @@ -198,6 +205,18 @@
> 921:
> .endm
>
> +/* Preserve the first 128-bits of Znz and zero the rest. */
> +.macro _sve_flush_z nz
> + _sve_check_zreg \nz
> + mov v\nz\().16b, v\nz\().16b
> +.endm
> +
> +.macro sve_flush
> + _for n, 0, 31, _sve_flush_z \n
> + _for n, 0, 15, _sve_pfalse \n
> + _sve_wrffr 0
Side note, but as and when hardware is available for benchmarking, it
could be worth investigating how sequences like this perform.
Because WRFFR is self-synchronising, it is a potentially expensive
operation; especially so if there could be in-flight SVE operations.
This isn't directly relevant to this patch, but could be worth a look
later on.
[...]
Cheers
---Dave
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next prev parent reply other threads:[~2020-07-15 16:53 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-29 13:35 [PATCH v3 0/8] arm64/sve: First steps towards optimizing syscalls Mark Brown
2020-06-29 13:35 ` [PATCH v3 1/8] arm64/fpsimd: Update documentation of do_sve_acc Mark Brown
2020-06-29 13:35 ` [PATCH v3 2/8] arm64/signal: Update the comment in preserve_sve_context Mark Brown
2020-06-29 13:35 ` [PATCH v3 3/8] arm64/fpsimdmacros: Allow the macro "for" to be used in more cases Mark Brown
2020-06-29 13:35 ` [PATCH v3 4/8] arm64/fpsimdmacros: Introduce a macro to update ZCR_EL1.LEN Mark Brown
2020-06-29 13:35 ` [PATCH v3 5/8] arm64/sve: Implement a helper to flush SVE registers Mark Brown
2020-07-15 16:52 ` Dave Martin [this message]
2020-06-29 13:35 ` [PATCH v3 6/8] arm64/sve: Implement a helper to load SVE registers from FPSIMD state Mark Brown
2020-07-15 16:52 ` Dave Martin
2020-06-29 13:35 ` [PATCH v3 7/8] arm64/sve: Don't disable SVE on syscalls return Mark Brown
2020-07-15 16:52 ` Dave Martin
2020-08-21 21:54 ` Mark Brown
2020-06-29 13:35 ` [PATCH v3 8/8] arm64/sve: Rework SVE trap access to use TIF_SVE_NEEDS_FLUSH Mark Brown
2020-07-15 16:52 ` Dave Martin
2020-07-15 16:49 ` [PATCH v3 0/8] arm64/sve: First steps towards optimizing syscalls Dave Martin
2020-07-15 17:11 ` Mark Brown
2020-07-20 10:44 ` Dave Martin
2020-07-21 2:43 ` zhang.lei
2020-07-21 22:34 ` Mark Brown
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