From: Arvind Sankar <nivedita@alum.mit.edu>
To: David Laight <David.Laight@ACULAB.COM>
Cc: 'Arvind Sankar' <nivedita@alum.mit.edu>,
Herbert Xu <herbert@gondor.apana.org.au>,
"David S. Miller" <davem@davemloft.net>,
"linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
Eric Biggers <ebiggers@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Eric Biggers <ebiggers@google.com>
Subject: Re: [PATCH v4 6/6] crypto: lib/sha256 - Unroll LOAD and BLEND loops
Date: Sun, 25 Oct 2020 19:53:49 -0400 [thread overview]
Message-ID: <20201025235349.GA1281192@rani.riverdale.lan> (raw)
In-Reply-To: <5d8f86fcfe84441fa5c9877959069ff1@AcuMS.aculab.com>
On Sun, Oct 25, 2020 at 11:23:52PM +0000, David Laight wrote:
> From: Arvind Sankar
> > Sent: 25 October 2020 20:18
> >
> > On Sun, Oct 25, 2020 at 06:51:18PM +0000, David Laight wrote:
> > > From: Arvind Sankar
> > > > Sent: 25 October 2020 14:31
> > > >
> > > > Unrolling the LOAD and BLEND loops improves performance by ~8% on x86_64
> > > > (tested on Broadwell Xeon) while not increasing code size too much.
> > >
> > > I can't believe unrolling the BLEND loop makes any difference.
> >
> > It's actually the BLEND loop that accounts for almost all of the
> > difference. The LOAD loop doesn't matter much in general: even replacing
> > it with a plain memcpy() only increases performance by 3-4%. But
> > unrolling it is low cost in code size terms, and clang actually does it
> > without being asked.
>
> (memcpy is wrong - misses the byte swaps).
I know it's wrong, the point is that it's impossible to gain very much
from optimizing the LOAD loop because it doesn't account for much of the
total time.
>
> That's odd, the BLEND loop is about 20 instructions.
> I wouldn't expect unrolling to help - unless you manage
> to use 16 registers for the active W[] values.
>
I am not sure about what's going on inside the hardware, but even with
a straightforward assembly version that just reads out of memory the way
the calculation is specified, unrolling the BLEND loop 8x speeds up the
performance by 7-8%.
The compiler is actually pretty bad here, just translating everything
into assembler with no attempt to optimize anything gets a 10-12%
speedup over the C version.
next prev parent reply other threads:[~2020-10-25 23:53 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-25 14:31 [PATCH v4 0/6] crypto: lib/sha256 - cleanup/optimization Arvind Sankar
2020-10-25 14:31 ` [PATCH v4 1/6] crypto: lib/sha256 - Use memzero_explicit() for clearing state Arvind Sankar
2020-10-26 7:59 ` Ard Biesheuvel
2020-10-25 14:31 ` [PATCH v4 2/6] crypto: " Arvind Sankar
2020-10-26 7:58 ` Ard Biesheuvel
2020-10-25 14:31 ` [PATCH v4 3/6] crypto: lib/sha256 - Don't clear temporary variables Arvind Sankar
2020-10-26 7:59 ` Ard Biesheuvel
2020-10-25 14:31 ` [PATCH v4 4/6] crypto: lib/sha256 - Clear W[] in sha256_update() instead of sha256_transform() Arvind Sankar
2020-10-26 8:00 ` Ard Biesheuvel
2020-10-25 14:31 ` [PATCH v4 5/6] crypto: lib/sha256 - Unroll SHA256 loop 8 times intead of 64 Arvind Sankar
2020-10-26 8:00 ` Ard Biesheuvel
2020-10-25 14:31 ` [PATCH v4 6/6] crypto: lib/sha256 - Unroll LOAD and BLEND loops Arvind Sankar
2020-10-25 18:51 ` David Laight
2020-10-25 20:18 ` Arvind Sankar
2020-10-25 23:23 ` David Laight
2020-10-25 23:53 ` Arvind Sankar [this message]
2020-10-26 10:06 ` David Laight
2020-10-26 8:02 ` Ard Biesheuvel
2020-10-30 6:53 ` [PATCH v4 0/6] crypto: lib/sha256 - cleanup/optimization Herbert Xu
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