[Mesa-dev] [PATCH] util: import sha1 implementation from OpenBSD

[Vladislav Egorov]

2017-01-13 22:43 GMT+03:00 Emil Velikov <emil.l.velikov at gmail.com>:
>
> On 13 January 2017 at 19:22, Vladislav Egorov <vegorov180 at gmail.com> wrote:
> > 13.01.2017 19:51, Emil Velikov пишет:
> >>
> >> From: Emil Velikov <emil.velikov at collabora.com>
> >>
> >> At the moment we support 5+ different implementations each with varying
> >> amount of bugs - from thread safely problems [1], to outright broken
> >> implementation(s) [2]
> >>
> >> In order to accommodate these we have 150+ lines of configure script and
> >> extra two configure toggles. Whist an actual implementation being
> >> ~200loc and our current compat wrapping ~250.
> >>
> >> Let's not forget that different people use different code paths, thus
> >> effectively makes it harder to test and debug since the default
> >> implementation is automatically detected.
> >>
> >> To minimise all these lovely experiences, import the "100% Public
> >> Domain" OpenBSD sha1 implementation. Clearly document any changes needed
> >> to get building correctly, since many/most of those can be upstreamed
> >> making future syncs easier.
> >
> >
> > It can hurt performance.
> This is not performance critical path ;-) If that ever changes we can
> rethink our options.
>
> Emil


If it's used by shader-cache, it's certainly along the critical path.
And 7-8 cycles per byte (or more than 10 cycles per byte on Atoms,
Celerons and low-end AMDs) per byte of shader text is something to be
considered. In comparison the entire preprocessing stage takes ~15
cycles per byte -- well, after my optimizations :) I regularly see
util_hash_crc32() in perf top - because it uses inefficient
table-based implementation with the same ~8 cycles per byte.