From: David Sterba <dsterba@suse.cz>
To: Wang Yugui <wangyugui@e16-tech.com>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: question about the performance of 'btrfs send'
Date: Mon, 17 Oct 2022 15:02:52 +0200 [thread overview]
Message-ID: <20221017130252.GN13389@twin.jikos.cz> (raw)
In-Reply-To: <20221015203501.E1ED.409509F4@e16-tech.com>
On Sat, Oct 15, 2022 at 08:35:01PM +0800, Wang Yugui wrote:
> Hi,
>
> a question about the performance of 'btrfs send'.
>
> The output speed of 'btrfs send' is about 700MiB/s in the 3 cases.
> 1) kernel 5.15.73 + 'btrfs send --proto 1'
> 2) kernel: 6.0.1(with btrfs-devel misc-6.1) + 'btrfs send --proto 1'
> 3) kernel: 6.0.1(with btrfs-devel misc-6.1) + 'btrfs send --proto 2'
> btrfs-progs: 6.0
>
> the outut of 'perf report':
> Overhead Command Shared Object Symbol
> *1 40.63% btrfs [kernel.kallsyms] [k] __crc32c_le
> *2 9.97% btrfs [kernel.kallsyms] [k] memcpy_erms
> *3 9.25% btrfs [kernel.kallsyms] [k] send_extent_data
> *4 5.40% btrfs [kernel.kallsyms] [k] asm_exc_nmi
> *5 2.73% btrfs [kernel.kallsyms] [k] __alloc_pages
> 1.14% btrfs [kernel.kallsyms] [k] __rmqueue_pcplist
> 0.92% btrfs [kernel.kallsyms] [k] bad_range
> 0.88% btrfs [kernel.kallsyms] [k] get_page_from_freelist
>
> What I expected:
> the above *1) __crc32c_le take >60%, and the outut speed > 1GiB/s.
> The *1) __crc32c_le is necessary operation, and the speed
> seems OK. 2GB/s * 40% = 800MiB/s, it is close to 700MiB/s.
>
> Question:
> The above *3) is difficult to understand. Any advice?
The perf report does not include IO, right? It's only CPU time spent.
That it's accounted only for send_extent_data would also mean there's
some function inlining involved so it does not point exactly where the
time is spent. I'd say it's the main loop around send_write that emits
the commands and works with memory data.
What could be suboptimal is the call get_cur_path in send_write that
rebuilds the path each time even though it's for the same file.
prev parent reply other threads:[~2022-10-17 13:03 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-15 12:35 question about the performance of 'btrfs send' Wang Yugui
2022-10-17 13:02 ` David Sterba [this message]
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