Re: Comparing rebase --am with --interactive via p3400

From: Elijah Newren <newren@gmail.com>
Date: Feb 1, 2019, 09:26 UTC
Message-ID: <CABPp-BF=ev03WgODk6TMQmuNoatg2kiEe5DR__gJ0OTVqHSnfQ@mail.gmail.com>
In-Reply-To: <nycvar.QRO.7.76.6.1901312310280.41@tvgsbejvaqbjf.bet>

Hi Dscho,

On Thu, Jan 31, 2019 at 10:04 PM Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:

Show 19 quoted lines

>
> Hi Elijah,
>
> as discussed at the Contributors' Summit, I ran p3400 as-is (i.e. with the
> --am backend) and then with --keep-empty to force the interactive backend
> to be used. Here are the best of 10, on my relatively powerful Windows 10
> laptop, with current `master`.
>
> With regular rebase --am:
>
> 3400.2: rebase on top of a lot of unrelated changes             5.32(0.06+0.15)
> 3400.4: rebase a lot of unrelated changes without split-index   33.08(0.04+0.18)
> 3400.6: rebase a lot of unrelated changes with split-index      30.29(0.03+0.18)
>
> with --keep-empty to force the interactive backend:
>
> 3400.2: rebase on top of a lot of unrelated changes             3.92(0.03+0.18)
> 3400.4: rebase a lot of unrelated changes without split-index   33.92(0.03+0.22)
> 3400.6: rebase a lot of unrelated changes with split-index      38.82(0.03+0.16)

Awesome, thanks for checking that out. I ran on both linux and mac and saw similar relative performances. Comparing am-based rebase to an implied-interactive rebase on both linux and mac (with a version of git including en/rebase-merge-on-sequencer so that -m gives the same performance that you'd see with --keep-empty), I saw:

On Linux:

am-based rebase (without -m):

3400.2: rebase on top of a lot of unrelated changes 1.87(1.64+0.21) 3400.4: rebase a lot of unrelated changes without split-index 7.87(6.24+1.00) 3400.6: rebase a lot of unrelated changes with split-index 5.99(5.05+0.67)

interactive-machinery rebase (with -m):

3400.2: rebase on top of a lot of unrelated changes 1.80(1.60+0.19) 3400.4: rebase a lot of unrelated changes without split-index 6.78(5.70+0.91) 3400.6: rebase a lot of unrelated changes with split-index 6.92(5.70+0.89)

On Mac:

am-based rebase (without -m):

Test this tree ------------------------------------------------------------------------------- 3400.2: rebase on top of a lot of unrelated changes 2.68(1.68+0.68) 3400.4: rebase a lot of unrelated changes without split-index 8.89(5.86+2.94) 3400.6: rebase a lot of unrelated changes with split-index 7.87(5.35+2.51)

interactive-machinery rebase (with -m):

Test this tree ------------------------------------------------------------------------------- 3400.2: rebase on top of a lot of unrelated changes 1.99(1.61+0.77) 3400.4: rebase a lot of unrelated changes without split-index 8.63(5.38+3.38) 3400.6: rebase a lot of unrelated changes with split-index 9.36(5.53+3.95)

Show 9 quoted lines

> I then changed it to -m to test the current scripted version, trying to
> let it run overnight, but my laptop eventually went to sleep and the tests
> were not even done. I'll let them continue and report back.
>
> My conclusion after seeing these numbers is: the interactive rebase is
> really close to the performance of the --am backend. So to me, it makes a
> total lot of sense to switch --merge over to it, and to make --merge the
> default. We still should investigate why the split-index performance is so
> significantly worse, though.

Cool, I'll update my patches to make --merge the default (building on top of en/rebase-merge-on-sequencer) and post it as an RFC. But yeah, we should also check into why the split-index performance becomes a bit worse with such a change.

Thanks, Elijah