From: "René Scharfe" <l.s.r@web.de>
To: Jeff King <peff@peff.net>
Cc: Git List <git@vger.kernel.org>, Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH 4/3] midx: inline nth_midxed_pack_entry()
Date: Sun, 12 Sep 2021 01:39:52 +0200 [thread overview]
Message-ID: <a96f8f25-46c6-5d61-6b3d-4b2da2e44566@web.de> (raw)
In-Reply-To: <YT0dgTgLVrtS9md6@coredump.intra.peff.net>
Am 11.09.21 um 23:20 schrieb Jeff King:
> On Sat, Sep 11, 2021 at 10:31:34PM +0200, René Scharfe wrote:
>
>> Am 11.09.21 um 19:07 schrieb Jeff King:
>>> On Sat, Sep 11, 2021 at 06:08:42PM +0200, René Scharfe wrote:
>>>
>>>> @@ -304,8 +307,7 @@ static int nth_midxed_pack_entry(struct repository *r,
>>>> if (!is_pack_valid(p))
>>>> return 0;
>>>>
>>>> - nth_midxed_object_oid(&oid, m, pos);
>>>> - if (oidset_contains(&p->bad_objects, &oid))
>>>> + if (oidset_contains(&p->bad_objects, oid))
>>>> return 0;
>>>
>>> So we get to avoid the nth_midxed_object_oid() copy entirely. Very nice.
>>>
>>> Compared to the code before your series, we still have an extra function
>>> call to oidset_contains(), which will (in the common case) notice we
>>> have no entries and immediately return. But I think that's getting into
>>> pointless micro-optimization.
>>
>> Right. I measure a 0.5% slowdown for git multi-pack-index verify. An
>> inline oidset_size call avoids it. That's easy enough to add, so let's
>> have it!
>
> I don't mind that, but I wonder if we can have our cake and eat it, too.
>
> oidset_contains() is short, too, and could be inlined. Or if we're
> worried about the size of the embedded kh_get_oid_set() getting inlined,
> we could do something like:
>
> static inline int oidset_contains(const struct oidset *set, const
> struct object_id *oid)
> {
> if (!oidset_size(set))
> return 0;
> return oidset_contains_func(set, oid);
> }
>
> That saves callers from having to deal with it, at the expense of a
> slightly complicated oidset implementation.
>
> I guess it's an extra integer comparison for callers that _do_ expect to
> have a non-empty set. So maybe it is better left to the caller to
> decide whether to optimize in this way.
>
> (A totally inline oidset_contains() avoids the extra check, but possibly
> at the cost of larger code size).
I wondered the same.
Inlining oidset_contains() would follow the spirit of khash. It adds
16KB to my build (ca. 688 bytes per caller). Hmm.
I expected the hybrid approach with an inlined emptiness check and a
shared actual contains function to be as fast as the original code, due
to caching. I actually saw the 0.1% slowdown of git multi-pack-index
verify when I added a fake bad object at the end of prepare_midx_pack()
to simulate a non-empty oidset. Hmm!
Both are probably defensible, but for this series I took the more
targeted approach to limit the impact.
René
next prev parent reply other threads:[~2021-09-11 23:40 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-11 7:50 [PATCH 0/3] packfile: use oidset for bad objects René Scharfe
2021-09-11 7:59 ` [PATCH 1/3] packfile: convert mark_bad_packed_object() to object_id René Scharfe
2021-09-11 8:00 ` [PATCH 2/3] packfile: convert has_packed_and_bad() " René Scharfe
2021-09-11 8:01 ` [PATCH 3/3] packfile: use oidset for bad objects René Scharfe
2021-09-11 14:26 ` Jeff King
2021-09-11 16:08 ` René Scharfe
2021-09-11 17:03 ` Jeff King
2021-09-11 17:16 ` René Scharfe
2021-09-11 14:27 ` [PATCH 0/3] " Jeff King
2021-09-11 16:08 ` [PATCH 4/3] midx: inline nth_midxed_pack_entry() René Scharfe
2021-09-11 17:03 ` René Scharfe
2021-09-11 17:07 ` Jeff King
2021-09-11 20:31 ` René Scharfe
2021-09-11 21:20 ` Jeff King
2021-09-11 23:39 ` René Scharfe [this message]
2021-09-11 20:31 ` [PATCH v2 0/5] packfile: use oidset for bad objects René Scharfe
2021-09-11 20:36 ` [PATCH 1/5] oidset: make oidset_size() an inline function René Scharfe
2021-09-11 20:39 ` [PATCH 2/5] midx: inline nth_midxed_pack_entry() René Scharfe
2021-09-11 20:40 ` [PATCH 3/5] packfile: convert mark_bad_packed_object() to object_id René Scharfe
2021-09-11 20:42 ` [PATCH v2 4/5] packfile: convert has_packed_and_bad() " René Scharfe
2021-09-11 20:43 ` [PATCH v2 5/5] packfile: use oidset for bad objects René Scharfe
2021-09-11 20:45 ` [PATCH v2 0/5] " René Scharfe
2021-09-11 21:22 ` Jeff King
2021-09-11 23:59 ` Derrick Stolee
2021-09-12 1:51 ` Taylor Blau
2021-09-12 2:29 ` Taylor Blau
2021-09-12 3:51 ` Derrick Stolee
2021-09-12 4:01 ` Taylor Blau
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