Re: [Qemu-devel] [PATCH 0/6] crypto: improve performance of XTS cipher mode

[Marc-André Lureau]

Hi

On Tue, Oct 9, 2018 at 6:13 PM Daniel P. Berrangé <address@hidden> wrote:
>
> On Tue, Oct 09, 2018 at 05:59:46PM +0400, Marc-André Lureau wrote:
> > Hi
> >
> > On Tue, Oct 9, 2018 at 4:57 PM Daniel P. Berrangé <address@hidden> wrote:
> > >
> > > The XTS cipher mode is significantly slower than CBC mode. This series
> > > approximately doubles the XTS performance which will improve the I/O
> > > rate for LUKS disks.
> > >
> > > Daniel P. Berrangé (6):
> > >   crypto: expand algorithm coverage for cipher benchmark
> > >   crypto: remove code duplication in tweak encrypt/decrypt
> > >   crypto: introduce a xts_uint128 data type
> > >   crypto: convert xts_tweak_encdec to use xts_uint128 type
> > >   crypto: convert xts_mult_x to use xts_uint128 type
> > >   crypto: annotate xts_tweak_encdec as inlineable
> > >
> > >  crypto/xts.c                    | 147 ++++++++++++++-----------------
> > >  tests/benchmark-crypto-cipher.c | 149 +++++++++++++++++++++++++++-----
> > >  2 files changed, 191 insertions(+), 105 deletions(-)
> >
> > By using a constant amount of data to process, it's easier to measure
> > perfomance with perf stat:
>
> The problem is that the different encryption modes have wildly
> different performance. eg while XTS gets 400 MB/s, ECB gets
> 3000 MB/s. I want the test to run long enough to minimize the
> noise, and picking a data size large enough for best ECB
> perf while not being excessively large for XTS is hard. THus
> I prefer to have a fixed execution time for each test.

I understand, I was just giving you some nice numbers to back your patches ;)

Otoh, I think having a fixed-size work for benchmark is more reliable,
even if the test runs quickly. I wouldn't rely on the current
benchmark results, they are quite unpredictable on my system.

>
> Regards,
> Daniel
> --
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-- 
Marc-André Lureau