From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: Jacob Vosmaer <jacob@gitlab.com>
Cc: git@vger.kernel.org
Subject: Re: [PATCH 1/1] upload-pack.c: make output buffer size configurable
Date: Tue, 14 Dec 2021 13:08:55 +0100 [thread overview]
Message-ID: <211214.86y24nbd46.gmgdl@evledraar.gmail.com> (raw)
In-Reply-To: <20211213132345.26310-2-jacob@gitlab.com>
On Mon, Dec 13 2021, Jacob Vosmaer wrote:
> Add a new compile time constant UPLOAD_PACK_BUFFER_SIZE that makes the
> size of the static buffer in output_state configurable.
>
> The current size of the buffer is 8192+1. The '+1' is a technical
> detail orthogonal to this change. On GitLab.com we use GitLab's
> pack-objects cache which does writes of 65515 bytes. Because of the
> default 8KB buffer size, propagating these cache writes requires 8
> pipe reads and 8 pipe writes from git-upload-pack, and 8 pipe reads
> from Gitaly (our Git RPC service). If we increase the size of the
> buffer to the maximum Git packet size, we need only 1 pipe read and 1
> pipe write in git-upload-pack, and 1 pipe read in Gitaly to transfer
> the same amount of data. In benchmarks with a pure fetch and 100%
> cache hit rate workload we are seeing CPU utilization reductions of
> over 30%.
>
> Signed-off-by: Jacob Vosmaer <jacob@gitlab.com>
> ---
> upload-pack.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/upload-pack.c b/upload-pack.c
> index c78d55bc67..b799fbe628 100644
> --- a/upload-pack.c
> +++ b/upload-pack.c
> @@ -42,6 +42,10 @@
> #define ALL_FLAGS (THEY_HAVE | OUR_REF | WANTED | COMMON_KNOWN | SHALLOW | \
> NOT_SHALLOW | CLIENT_SHALLOW | HIDDEN_REF)
>
> +#ifndef UPLOAD_PACK_BUFFER_SIZE
> +#define UPLOAD_PACK_BUFFER_SIZE 8192
> +#endif
> +
> /* Enum for allowed unadvertised object request (UOR) */
> enum allow_uor {
> /* Allow specifying sha1 if it is a ref tip. */
> @@ -194,7 +198,7 @@ static int write_one_shallow(const struct commit_graft *graft, void *cb_data)
> }
>
> struct output_state {
> - char buffer[8193];
> + char buffer[UPLOAD_PACK_BUFFER_SIZE+1];
> int used;
> unsigned packfile_uris_started : 1;
> unsigned packfile_started : 1;
Making this configurable obviousl has big impact in some cases, but I'm
a bit iffy on the faciltity to do so + it not being documented.
I don't think that the "static buffer" part here is important to anyone,
but the write() size is clearly important.
So doesn't it make more sense to have a uploadPack.bufferSize=8k
variable we can tweak, just make this "buffer" a "struct strbuf" instead
(i.e. it'll by dynamically grown), and then just flush it whenever we
hit the configured buffer size?
next prev parent reply other threads:[~2021-12-14 12:11 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-13 13:23 [PATCH 0/1] Make upload-pack pack write size configurable Jacob Vosmaer
2021-12-13 13:23 ` [PATCH 1/1] upload-pack.c: make output buffer " Jacob Vosmaer
2021-12-14 12:08 ` Ævar Arnfjörð Bjarmason [this message]
2021-12-14 15:08 ` Jeff King
2021-12-14 19:46 ` [PATCH v2 0/1] upload-pack.c: increase output buffer size Jacob Vosmaer
2021-12-14 19:46 ` [PATCH v2 1/1] " Jacob Vosmaer
2021-12-14 20:41 ` Ævar Arnfjörð Bjarmason
2021-12-15 16:30 ` Jeff King
2021-12-15 19:50 ` Junio C Hamano
2021-12-15 19:59 ` rsbecker
2021-12-15 20:24 ` Jacob Vosmaer
2021-12-15 20:38 ` rsbecker
2021-12-15 20:45 ` Jacob Vosmaer
2021-12-15 21:34 ` rsbecker
2021-12-14 15:37 ` [PATCH 1/1] upload-pack.c: make output buffer size configurable Jeff King
2021-12-14 20:04 ` Jacob Vosmaer
2021-12-14 15:12 ` [PATCH 0/1] Make upload-pack pack write " Jeff King
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