From: Eric Biggers <ebiggers@kernel.org>
To: Ignat Korchagin <ignat@cloudflare.com>
Cc: agk@redhat.com, Mike Snitzer <snitzer@redhat.com>,
dm-devel@redhat.com, dm-crypt@saout.de,
linux-kernel <linux-kernel@vger.kernel.org>,
kernel-team <kernel-team@cloudflare.com>
Subject: Re: [dm-crypt] [RFC PATCH 1/1] Add DM_CRYPT_FORCE_INLINE flag to dm-crypt target
Date: Wed, 24 Jun 2020 09:24:07 -0700 [thread overview]
Message-ID: <20200624162407.GB200774@gmail.com> (raw)
In-Reply-To: <CALrw=nFduv_X83V1Dfz+bt4bZqT19OSi3q5f7umhty1-DQ2SPg@mail.gmail.com>
On Wed, Jun 24, 2020 at 09:24:07AM +0100, Ignat Korchagin wrote:
> On Wed, Jun 24, 2020 at 6:04 AM Eric Biggers <ebiggers@kernel.org> wrote:
> >
> > On Fri, Jun 19, 2020 at 05:41:32PM +0100, Ignat Korchagin wrote:
> > > Sometimes extra thread offloading imposed by dm-crypt hurts IO latency. This is
> > > especially visible on busy systems with many processes/threads. Moreover, most
> > > Crypto API implementaions are async, that is they offload crypto operations on
> > > their own, so this dm-crypt offloading is excessive.
> >
> > This really should say "some Crypto API implementations are async" instead of
> > "most Crypto API implementations are async".
>
> The most accurate would probably be: most hardware-accelerated Crypto
> API implementations are async
>
> > Notably, the AES-NI implementation of AES-XTS is synchronous if you call it in a
> > context where SIMD instructions are usable. It's only asynchronous when SIMD is
> > not usable. (This seems to have been missed in your blog post.)
>
> No, it was not. This is exactly why we made xts-proxy Crypto API
> module as a second patch. But it seems now it does not make a big
> difference if a used Crypto API implementation is synchronous as well
> (based on some benchmarks outlined in the cover letter to this patch).
> I think the v2 of this patch will not require a synchronous Crypto
> API. This is probably a right thing to do, as the "inline" flag should
> control the way how dm-crypt itself handles requests, not how Crypto
> API handles requests. If a user wants to ensure a particular
> synchronous Crypto API implementation, they can already reconfigure
> dm-crypt and specify the implementation with a "capi:" prefix in the
> the dm table description.
I think you're missing the point. Although xts-aes-aesni has the
CRYPTO_ALG_ASYNC bit set, the actual implementation processes the request
synchronously if SIMD instructions are currently usable. That's always the case
in dm-crypt, as far as I can tell. This algorithm has the ASYNC flag only
because it's not synchronous when called in hardIRQ context.
That's why your "xts-proxy" doesn't make a difference, and why it's misleading
to suggest that the crypto API is doing its own queueing when you're primarily
talking about xts-aes-aesni. The crypto API definitely can do its own queueing,
mainly with hardware drivers. But it doesn't in this common and relevant case.
- Eric
next prev parent reply other threads:[~2020-06-24 16:24 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-19 16:41 [RFC PATCH 0/1] dm-crypt excessive overhead Ignat Korchagin
2020-06-19 16:41 ` [RFC PATCH 1/1] Add DM_CRYPT_FORCE_INLINE flag to dm-crypt target Ignat Korchagin
2020-06-24 5:04 ` [dm-crypt] " Eric Biggers
2020-06-24 5:21 ` [dm-devel] " Damien Le Moal
2020-06-24 5:27 ` Eric Biggers
2020-06-24 6:46 ` Damien Le Moal
2020-06-24 7:24 ` Damien Le Moal
2020-06-24 7:49 ` Damien Le Moal
2020-06-24 8:24 ` Ignat Korchagin
2020-06-24 16:24 ` Eric Biggers [this message]
2020-06-24 17:00 ` Ignat Korchagin
2020-06-24 5:12 ` [dm-devel] " Damien Le Moal
2020-06-19 16:55 ` [RFC PATCH 0/1] dm-crypt excessive overhead Mike Snitzer
2020-06-19 18:39 ` Mikulas Patocka
2020-06-19 19:44 ` Ignat Korchagin
2020-06-20 1:23 ` Herbert Xu
2020-06-20 19:36 ` Mikulas Patocka
2020-06-20 21:02 ` Ignat Korchagin
2020-06-23 15:33 ` Mike Snitzer
2020-06-23 16:24 ` Ignat Korchagin
2020-06-24 0:23 ` Herbert Xu
2020-06-22 0:45 ` [dm-devel] " Damien Le Moal
2020-06-22 7:55 ` Ignat Korchagin
2020-06-22 8:08 ` Damien Le Moal
2020-06-23 15:01 ` Mike Snitzer
2020-06-23 15:07 ` Ignat Korchagin
2020-06-23 15:22 ` Mike Snitzer
2020-06-24 4:54 ` [dm-devel] " Damien Le Moal
2020-06-24 5:22 ` Mike Snitzer
2020-06-24 8:02 ` Ignat Korchagin
2020-06-24 4:28 ` Damien Le Moal
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