Ben Peart <benpeart@xxxxxxxxxxxxx> writes:
> On further investigation with the previous patch, I noticed that my test
> repos didn't contain the cache tree extension in their index. After doing a
> commit to ensure they existed, I realized that in some instances, the time
> to load the cache tree exceeded the time to load all the cache entries in
> parallel. Because the thread to read the cache tree was started last (due
> to having to parse through all the cache entries first) we weren't always
> getting optimal performance.
>
> To better optimize for this case, I decided to write the EOIE extension
> as suggested by Junio [1] in response to my earlier multithreading patch
> series [2]. This enables me to spin up the thread to load the extensions
> earlier as it no longer has to parse through all the cache entries first.
Hmph. I kinda liked the simplicity of the previous one, but if we
need to start reading the extension sections sooner by eliminating
the overhead to scan the cache entries, perhaps we should bite the
bullet now.
> The big changes in this iteration are:
>
> - add the EOIE extension
> - update the index extension worker thread to start first
I guess I'd need to see the actual patch to find this out, but once
we rely on a new extension, then we could omit scanning the main
index even to partition the work among workers (i.e. like the topic
long ago, you can have list of pointers into the main index to help
partitioning, plus reset the prefix compression used in v4). I
think you didn't get that far in this round, which is good. If the
gain with EOIE alone (and starting the worker for the extension
section early) is large enough without such a pre-computed work
partition table, the simplicity of this round may give us a good
stopping point.
> This patch conflicts with Duy's patch to remove the double memory copy and
> pass in the previous ce instead. The two will need to be merged/reconciled
> once they settle down a bit.
Thanks. I have a feeling that 67922abb ("read-cache.c: optimize
reading index format v4", 2018-09-02) is already 'next'-worthy
and ready to be built on, but I'd prefer to hear from Duy to double
check.
