On Wed, Feb 12, 2014 at 12:06 PM, Junio C Hamano <gits...@pobox.com> wrote:
> Stefan Zager <sza...@chromium.org> writes:
>> ... I used the Very Sleepy profiler
>> to see where all the time was spent on Windows: 55% of the time was
>> spent in OpenFile, and 25% in CloseFile (both in win32).
> This is somewhat interesting.
> When we check things out, checkout_paths() has a list of paths to be
> checked out, and iterates over them and call checkout_entry().
> I wonder if you can:
> - introduce a version of checkout_entry() that takes file
> descriptors to write to;
> - have an asynchronous helper threads that pre-open the paths to be
> written out and feed <ce, file descriptor to be written> to a
> - restructure that loop so that it reads the <ce, file descriptor
> to be written> from the queue, performs the actual writing out,
> and then feeds <file descriptor to be closed> to another queue; and
> - have another asynchronous helper threads that reads <file
> descriptor to be closed> from the queue and close them.
> Calls to write (and preparation of data to be written) will then
> remain single-threaded, but it sounds like that codepath is not the
> bottleneck in your measurement, so....
Yes, I considered that as well. At a minimum, that would still
require attr.c to implement thread locking, since attribute files must
be parsed to look for stream filters. I have already done that work.
But I'm not sure it's the best long-term approach to add convoluted
custom threading solutions to each git operation as it appears on the
performance radar. I'm hoping to make the entire code base more
thread-friendly, so that threading can be added in a more natural and
idiomatic (and less painful) way.
For example, the most natural way to add threading to checkout would
be in the loops over the index in check_updates() in unpack-trees.c.
If attr.c and sha1_file.c were thread-safe, then it would be possible
to thread checkout entirely in check_updates(), with a pretty compact
code change. I have already done the work in attr.c; sha1_file.c is
hairier, but do-able.
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