From: Elijah Newren <newren@gmail.com>
To: Taylor Blau <ttaylorr@github.com>
Cc: Git Mailing List <git@vger.kernel.org>,
Derrick Stolee <dstolee@microsoft.com>, Jeff King <peff@peff.net>,
Jonathan Nieder <jrnieder@gmail.com>,
Jonathan Tan <jonathantanmy@google.com>,
Taylor Blau <me@ttaylorr.com>
Subject: Re: [PATCH 1/1] merge-ort: begin performance work; instrument with trace2_region_* calls
Date: Fri, 8 Jan 2021 13:50:34 -0800 [thread overview]
Message-ID: <CABPp-BE4zyGa7=dOKifWhv-46__0YtfRZ39Q1JYT0JZ2HT0itA@mail.gmail.com> (raw)
In-Reply-To: <X/jHpZlSxwAxoUyq@nand.local>
On Fri, Jan 8, 2021 at 12:59 PM Taylor Blau <ttaylorr@github.com> wrote:
>
> On Fri, Jan 08, 2021 at 12:51:11PM -0800, Elijah Newren wrote:
> > Overall timings, using hyperfine (1 warmup run, 3 runs for mega-renames,
> > 10 runs for the other two cases):
>
> Ah, I love hyperfine. In case you don't already have this in your
> arsenal, the following `--prepare` step is useful for measuring
> cold-cache performance:
>
> --prepare='sync; echo 3 | sudo tee /proc/sys/vm/drop_caches'
/proc/sys/vm/drop_caches is definitely useful for cold-cache
measurements and I've used it in other projects for that purpose. I
think cold-cache testing makes sense for various I/O intensive areas
such as object lookup, but I ignored it here as I felt the merge code
is really about algorithmic performance. So, I instead went the other
direction and ensured warm-cache testing by using a warmup run, in
order to ensure that I wasn't putting one of the tests at an unfair
disadvantage. (Side note: My script that runs the tests actually does
more than the warmup run to ensure a fair playing field. For example,
the script expires reflogs and runs a git prune before each hyperfine
invocation, to make sure that each hyperfine run starts with a fully
repacked repository with no loose objects. Without the expire &
prune, enough perf testing of rebases in a short time period will
result in a mysterious and gradual slowdown of all the test runs even
without code changes...).
> > === Goals ===
> >
> > This patch is obviously just the beginning. Here are some of my goals
> > that this measurement will help us achieve:
> >
> > * Drive the cost of rename detection down considerably for merges
> > * After the above has been achieved, see if there are other slowness
> > factors (which would have previously been overshadowed by rename
> > detection costs) which we can then focus on and also optimize.
> > * Ensure our rebase testcase that requires little rename detection
> > is noticeably faster with merge-ort than with apply-based rebase.
>
> These are great, and I am looking forward to your work.
>
> > Signed-off-by: Elijah Newren <newren@gmail.com>
>
> Thanks, this patch looks good to me.
As always, thanks for taking a look.
next prev parent reply other threads:[~2021-01-08 21:57 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-08 20:51 [PATCH 0/1] And so it begins...merge/rename performance work Elijah Newren
2021-01-08 20:51 ` [PATCH 1/1] merge-ort: begin performance work; instrument with trace2_region_* calls Elijah Newren
2021-01-08 20:59 ` Taylor Blau
2021-01-08 21:50 ` Elijah Newren [this message]
2021-01-08 21:55 ` Taylor Blau
2021-01-09 0:52 ` Elijah Newren
2021-01-13 22:11 ` [PATCH v2 0/1] And so it begins...merge/rename performance work Elijah Newren
2021-01-13 22:11 ` [PATCH v2 1/1] merge-ort: begin performance work; instrument with trace2_region_* calls Elijah Newren
2021-01-14 19:08 ` [PATCH v2 0/1] And so it begins...merge/rename performance work Junio C Hamano
2021-01-14 20:18 ` Elijah Newren
2021-01-15 19:29 ` [PATCH v3 " Elijah Newren
2021-01-15 19:29 ` [PATCH v3 1/1] merge-ort: begin performance work; instrument with trace2_region_* calls Elijah Newren
2021-01-24 6:01 ` [PATCH v4 0/3] And so it begins...merge/rename performance work Elijah Newren
2021-01-24 6:01 ` [PATCH v4 1/3] merge-ort: fix massive leak Elijah Newren
2021-01-24 19:11 ` Derrick Stolee
2021-01-24 6:01 ` [PATCH v4 2/3] merge-ort: ignore the directory rename split conflict for now Elijah Newren
2021-01-24 6:01 ` [PATCH v4 3/3] merge-ort: begin performance work; instrument with trace2_region_* calls Elijah Newren
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