From: nicolas.pitre@linaro.org (Nicolas Pitre)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH RFC 0/3] arm64: NEON crypto under CONFIG_PREEMPT
Date: Fri, 28 Mar 2014 22:03:19 -0400 (EDT) [thread overview]
Message-ID: <alpine.LFD.2.11.1403282155290.1571@knanqh.ubzr> (raw)
In-Reply-To: <1396004735-15475-1-git-send-email-ard.biesheuvel@linaro.org>
On Fri, 28 Mar 2014, Ard Biesheuvel wrote:
> This series is an attempt to reduce latency under CONFIG_PREEMPT while
> maintaining optimal throughput otherwise, i.e., under !CONFIG_PREEMPT or
> while running outside of process context.
>
> In the in_interrupt() case, the calls to kernel_neon_begin and kernel_neon_end
> incur a fixed penalty (i.e., each call needs to stack/unstack a fixed number of
> registers), and preemption is not possible anyway, so the call into the crypto
> algorithm should just complete as fast as possible, ideally by processing all
> of the input in the core loop without having to spill state to memory or reload
> round keys (e.g., SHA-256 uses 64 32-bit round keys to process each input block
> of 64 bytes)
>
> In contrast, when running in process context, we should avoid hogging the CPU by
> spending unreasonable amounts of time inside a kernel_neon_begin/kernel_neon_end
> section. However, reloading those 64 32-byte round keys to process each 64-byte
> block one by one is far from optimal.
>
> The solution proposed here is to allow the inner loops of the crypto algorithms
> to test the TIF_NEED_RESCHED flag, and terminate early if it is set. This is
> essentially CONFIG_PREEMPT_VOLUNTARY, even under CONFIG_PREEMPT, but it is the
> best we can do when running with preemption disabled.
>
> Patch #1 introduces the shared asm macro, patches #2 and #3 are the SHA-1 and
> SHA-224/SHA-256 implementations I posted earlier, but reworked to utilize
> voluntary preemption.
How extensive is the required rework? If reasonably small, I think this
would be better to have #2 and #3 as patches to be applied on top of
your initial implementations instead. It helps with patch review, and
it makes it easier in the occurrence of a problem to tell users to just
revert commit xyz in order to get the SHA code without voluntary
preemption for testing.
Nicolas
next prev parent reply other threads:[~2014-03-29 2:03 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-28 11:05 [PATCH RFC 0/3] arm64: NEON crypto under CONFIG_PREEMPT Ard Biesheuvel
2014-03-28 11:05 ` [PATCH RFC 1/3] arm64/crypto: add shared macro to test for NEED_RESCHED Ard Biesheuvel
2014-03-29 1:53 ` Nicolas Pitre
2014-03-31 19:07 ` Ard Biesheuvel
2014-03-28 11:05 ` [PATCH RFC 2/3] arm64/crypto: SHA-1 using ARMv8 Crypto Extensions Ard Biesheuvel
2014-03-28 11:05 ` [PATCH RFC 3/3] arm64/crypto: SHA-224/SHA-256 " Ard Biesheuvel
2014-03-29 2:03 ` Nicolas Pitre [this message]
2014-03-31 19:04 ` [PATCH RFC 0/3] arm64: NEON crypto under CONFIG_PREEMPT Ard Biesheuvel
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