Re: [PATCH 14/19] [GSOC] cat-file: reuse ref-filter logic

From: ZheNing Hu <adlternative@gmail.com>
Date: Jul 14, 2021, 16:24 UTC
Message-ID: <CAOLTT8RR4+tUuT2yc2PDL9NwCburW8bM_Sht6nhKJ_fYV8fGsQ@mail.gmail.com>
In-Reply-To: <xmqqtukz2rp4.fsf@gitster.g>

Junio C Hamano <gitster@pobox.com> 于2021年7月13日周二 上午4:38写道：

Show 11 quoted lines

>
> Christian Couder <christian.couder@gmail.com> writes:
>
> More importantly, why is such a fast-path even needed?  Isn't it a
> sign that the ref-filter implementation is eating more cycles than
> it should for given set of placeholders?  Do we know where the extra
> cycles goes?
>
> I find it somewhat alarming if we are talking about "fast-path"
> workaround before understanding why we are seeing slowdown in the
> first place.

There is no complete conclusion yet, but I try to use time and hyperfine test for these commits (t/perf/* is not accurate enough):

----------------------------------------------------------------------------------------------------------------------------
|                        subject                                  |
--batch-check (using hyperfine) |   --batch(using time) |
----------------------------------------------------------------------------------------------------------------------------
|[GSOC] cat-file: use fast path when using default_format         |
        700ms                |          25.450s      |
----------------------------------------------------------------------------------------------------------------------------
|[GSOC] cat-file: re-implement --textconv, --filters options      |
        790ms                |          29.933s      |
----------------------------------------------------------------------------------------------------------------------------
|[GSOC] cat-file: reuse err buf in batch_object_write()           |
        770ms                |          29.153s      |
----------------------------------------------------------------------------------------------------------------------------
|[GSOC] cat-file: reuse ref-filter logic                          |
        780ms                |          29.412s      |
----------------------------------------------------------------------------------------------------------------------------
|The third batch (upstream/master)                                |
        640ms                |          26.025s      |
----------------------------------------------------------------------------------------------------------------------------

I think we their cost is indeed from "[GSOC] cat-file: reuse ref-filter logic". But what causes the loss of performance needs further analysis.

Thanks. -- ZheNing Hu