Re: [PATCH v3 30/30] t/perf: implement performace tests for pseudo-merge bitmaps

From: Jeff King <peff@peff.net>
Date: May 25, 2024, 03:13 UTC
Message-ID: <20240525031317.GA1889620@coredump.intra.peff.net>
In-Reply-To: <Zk+epE2S4KErPyVk@nand.local>

On Thu, May 23, 2024 at 03:53:08PM -0400, Taylor Blau wrote:

> -	GIT_TEST_USE_PSEDUO_MERGES=0 \
> +	GIT_TEST_USE_PSEUDO_MERGES=0 \

Whoops.

Show 10 quoted lines

> Sure enough, that shows us a little gap between the "no pseudo-merges"
> and "with pseudo-merges" case:
> 
> ```
> Test                                                                this tree
> -----------------------------------------------------------------------------------
> 5333.2: git rev-list --count --all --objects (no bitmaps)           3.54(3.45+0.08)
> 5333.3: git rev-list --count --all --objects (no pseudo-merges)     0.43(0.40+0.03)
> 5333.4: git rev-list --count --all --objects (with pseudo-merges)   0.12(0.11+0.01)
> ```

OK, that seems more like it. 300ms is nice, but there's just not that much improvement to make here.

This one is much more exciting:

Show 7 quoted lines

> ```
> Test                                                                this tree
> ---------------------------------------------------------------------------------------
> 5333.1: git rev-list --count --all --objects (no bitmaps)           122.29(121.31+0.97)
> 5333.2: git rev-list --count --all --objects (no pseudo-merges)     21.88(21.30+0.58)
> 5333.3: git rev-list --count --all --objects (with pseudo-merges)   5.05(4.77+0.28)
> ```

Very nice improvement.

I wonder what we spend the final 5s on. Maybe just book-keeping to assemble all the tips (and maybe even parse tip commits? I can't remember if we ever optimized that out). Anyway, that's all out of scope for your series. Getting rid of the expensive traversal would let us focus on those final bits. ;)

-Peff