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From: Junio C Hamano <gitster@pobox.com>
To: Jeff Hostetler <git@jeffhostetler.com>
Cc: Christian Couder <christian.couder@gmail.com>,
	git@vger.kernel.org, Jeff Hostetler <jeffhost@microsoft.com>,
	Jonathan Tan <jonathantanmy@google.com>,
	Derrick Stolee <stolee@gmail.com>, Kevin Daudt <me@ikke.info>,
	Christian Couder <chriscool@tuxfamily.org>
Subject: Re: [PATCH v2 2/2] sha1_file: improve sha1_file_name() perfs
Date: Wed, 17 Jan 2018 12:54:33 -0800	[thread overview]
Message-ID: <xmqq4lnkryt2.fsf@gitster.mtv.corp.google.com> (raw)
In-Reply-To: <3cbace45-61df-3074-a48c-66c68c96d542@jeffhostetler.com> (Jeff Hostetler's message of "Wed, 17 Jan 2018 15:37:55 -0500")

Jeff Hostetler <git@jeffhostetler.com> writes:

>>     void sha1_file_name(struct strbuf *buf, const unsigned char
>> *sha1)
>>   {
>> -	strbuf_addf(buf, "%s/", get_object_directory());
>> +	const char *obj_dir = get_object_directory();
>> +	size_t extra = strlen(obj_dir) + 1 + GIT_MAX_HEXSZ;
>
> Very minor nit.  Should this be "+3" rather than "+1"?
> One for the slash after obj_dir, one for the slash between
> "xx/y[38]", and one for the trailing NUL.
>
>>   +	if (extra > strbuf_avail(buf))
>> +		strbuf_grow(buf, extra);

The callers who care use static strbuf with 1/2, which lets them
grow it to an appropriate size after they make their first call.

On the other hand, the ones to which performance does not matter by
definition do not care.

I actually think this whole "extra -> grow" business should be
discarded.  With a miscomputed "extra" like this, it does not help
anybody---everybody may pay cost for one extra realloc due to the
miscalculation, and the ones that do care also do during their first
call.



  reply	other threads:[~2018-01-17 20:54 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-17 17:54 [PATCH v2 1/2] sha1_file: remove static strbuf from sha1_file_name() Christian Couder
2018-01-17 17:54 ` [PATCH v2 2/2] sha1_file: improve sha1_file_name() perfs Christian Couder
2018-01-17 20:37   ` Jeff Hostetler
2018-01-17 20:54     ` Junio C Hamano [this message]
2018-01-17 22:27       ` Jeff King
2018-01-17 21:44     ` Christian Couder

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