On Fri, Mar 21, 2014 at 4:56 AM, Stefan Zager <sza...@chromium.org> wrote:
>> Considering all that, Duy's solution of opening separate file descriptors 
>> per thread seems to be the best pattern for future multi-threaded work.
> Does that mean you would endorse the (N threads) * (M pack files)
> approach to threading checkout and status?  That seems kind of
> crazy-town to me.  Not to mention that pack windows are not shared, so
> this approach to multi-threading can have the side-effect of blowing
> out memory consumption.

Maybe we could protect and share the delta cache. Pack windows are
mmap'd so we should not need to worry about their memory consumption.

> We have already had to dial back settings for
> pack.threads and core.deltaBaseCacheLimit, because threaded index-pack
> was causing OOM errors on 32-bit platforms.

Hm.. I don't think index-pack uses sha1_file.c heavily. Local pack
access is only needed for verifying identical objects (and that should
never happen often). Something is fishy with these OOM errors.

> Cygwin (and MSVC) should be able to share a "mostly" compliant pread
> implementation.  I don't have any insight into NonstopKernel; does is
> really not have a thread-safe pread implementation?  If so, then I
> suppose we have to #ifdef NO_PREAD, just as we do now.
> I realize that these are deep changes.  However, the performance of
> msysgit on the chromium repositories is pretty awful, enough so to
> motivate this work.
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