From: Mark Brown <broonie@kernel.org>
To: Dave Martin <Dave.Martin@arm.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Ard Biesheuvel <ardb@kernel.org>,
l00374334 <liqiang64@huawei.com>,
Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
Maxime Coquelin <mcoquelin.stm32@gmail.com>,
Will Deacon <will@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Herbert Xu <herbert@gondor.apana.org.au>
Subject: Re: [PATCH 1/1] arm64: Accelerate Adler32 using arm64 SVE instructions.
Date: Wed, 4 Nov 2020 18:49:05 +0000 [thread overview]
Message-ID: <20201104184905.GB4812@sirena.org.uk> (raw)
In-Reply-To: <20201104181256.GG6882@arm.com>
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On Wed, Nov 04, 2020 at 06:13:06PM +0000, Dave Martin wrote:
> On Wed, Nov 04, 2020 at 05:50:33PM +0000, Mark Brown wrote:
> > I think at a minimum we'd want to handle the vector length explicitly
> > for kernel mode SVE, vector length independent code will work most of
> > the time but at the very least it feels like a landmine waiting to cause
> > trouble. If nothing else there's probably going to be cases where it
> > makes a difference for performance. Other than that I'm not currently
...
> The main reasons for constraining the vector length are a) to hide
> mismatches between CPUs in heterogeneous systems, b) to ensure that
> validated software doesn't run with a vector length it wasn't validated
> for, and c) testing.
> For kernel code, it's reasonable to say that all code should be vector-
> length agnostic unless there's a really good reason not to be. So we
> may not care too much about (b).
> In that case, just setting ZCR_EL1.LEN to max in kernel_sve_begin() (or
> whatever) probably makes sense.
I agree, that's most likely a good default.
> For (c), it might be useful to have a command-line parameter or debugfs
> widget to constrain the vector length for kernel code; perhaps globally
> or perhaps per driver or algo.
I think a global control would be good for testing, it seems simpler and
easier all round. The per thing tuning seems more useful for cases
where we run into something like a performance reason to use a limited
set of vector lengths but I think we should only add that when we have
at least one user for it, some examples of actual restrictions we want
would probably be helpful for designing the interface.
> Nonetheless, working up a candidate algorithm to help us see whether
> there is a good use case seems like a worthwhile project, so I don't
> want to discourage that too much.
Definitely worth exploring.
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next prev parent reply other threads:[~2020-11-04 18:51 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-03 12:15 [PATCH 0/1] arm64: Accelerate Adler32 using arm64 SVE instructions l00374334
2020-11-03 12:15 ` [PATCH 1/1] " l00374334
2020-11-03 14:34 ` Ard Biesheuvel
2020-11-03 18:00 ` Dave Martin
2020-11-04 9:19 ` Li Qiang
2020-11-04 14:49 ` Dave Martin
2020-11-05 2:32 ` Li Qiang
2020-11-04 17:50 ` Mark Brown
2020-11-04 18:13 ` Dave Martin
2020-11-04 18:49 ` Mark Brown [this message]
2020-11-05 17:56 ` Dave Martin
2020-11-04 8:01 ` Li Qiang
2020-11-04 8:04 ` Ard Biesheuvel
2020-11-04 8:14 ` Li Qiang
2020-11-04 17:57 ` Eric Biggers
2020-11-05 2:49 ` Li Qiang
2020-11-05 7:51 ` Ard Biesheuvel
2020-11-05 9:05 ` Li Qiang
2020-11-05 18:21 ` Eric Biggers
2020-11-09 6:29 ` Li Qiang
2020-11-05 16:53 ` [PATCH 0/1] " Dave Martin
2020-11-09 3:43 ` Li Qiang
2020-11-10 10:46 ` Dave Martin
2020-11-10 13:20 ` Li Qiang
2020-11-10 16:07 ` Dave Martin
2020-11-12 7:20 ` Li Qiang
2020-11-12 11:17 ` Dave Martin
2020-11-14 7:31 ` Li Qiang
2020-11-16 15:56 ` Dave Martin
2020-11-17 12:45 ` Li Qiang
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