Hi, On Thu, 28 Dec 2017, Ævar Arnfjörð Bjarmason wrote: > On Wed, Dec 27 2017, Jonathan Nieder jotted: > > > +git-for-windows > > Ævar Arnfjörð Bjarmason wrote: > > > >> Using BLK_SHA1 in lieu of the OpenSSL routines was done in [1], but > >> since DC_SHA1 is now the default for git in general it makes sense for > >> Windows to use that too, this looks like something that was missed > >> back in [2]. > >> > >> As noted in [3] OpenSSL has a performance benefit compared to BLK_SHA1 > >> on MinGW, so perhaps that and the Windows default should be changed > >> around again, but that's a topic for another series, it seems clear > >> that this specific flag is nobody's explicit intention. > > > > I have some memory of performance issues on Windows when DC_SHA1 was > > introduced leading to interest in a mixed configuration with DC_SHA1 > > only being used where it is security sensitive (e.g. for object naming > > but not for packfile trailers). > > > > Did anything come of that? > > This was Johannes Schindelin (CC'd) on-list when the sha1dc discussion > first came up earlier this year. I.e. it's slower, so we could use > openssl on trusted data and sha1dc on untrusted data, but nothing came > of that. The performance degradation is noticeable, as far as I can see. And no, we have not yet worked on the hyprid SHA-1-DC solution, as we expect bigger benefits from trying to avoid unnecessary SHA-1 calculation to begin with (read: we will try to catch bigger fish first). All of this may also become moot if we ever get off the ground with SHA-256 (or whatever we will use then). Ciao, Dscho
