From: Thomas Lamprecht <t.lamprecht@proxmox.com>
To: Proxmox VE development discussion <pve-devel@lists.proxmox.com>,
Filip Schauer <f.schauer@proxmox.com>
Subject: [pve-devel] applied: [PATCH v2 common] tools: file_set_contents: use syswrite instead of print
Date: Mon, 14 Oct 2024 10:42:02 +0200 [thread overview]
Message-ID: <e4a78a89-9b1d-48e0-8609-556752457ac4@proxmox.com> (raw)
In-Reply-To: <20240930114045.76730-1-f.schauer@proxmox.com>
Am 30/09/2024 um 13:40 schrieb Filip Schauer:
> The use of `print` can be inefficient for writing larger files due to
> its default buffering in 8 KiB blocks.
>
> This is especially problematic on `pmxcfs` where files are written in
> 4 KiB blocks due to the defaults of `libfuse2`. This leads to
> significant write amplification on files larger than 4 KiB.
>
> Patch (fix #5728: pmxcfs: allow bigger writes than 4k for fuse) [1]
> addresses this by enabling `big_writes`, allowing up to 128 KiB blocks.
> But due to the use of `print` in `file_set_contents`, writes are still
> only buffered in 8 KiB blocks.
>
> To further address this, this commit switches to using `syswrite`
> instead of `print` to mitigate the block size limit imposed by `print`.
> Combined with patch [1], file writes to `/etc/pve/` are now buffered in
> 128 KiB blocks.
>
> The table below illustrates the drastic reduction in write
> amplification when writing files of different sizes to `/etc/pve/` using
> `file_set_contents`:
>
> print big_writes+print big_writes+syswrite
> file size written amplif. written amplif. written amplif.
> 1 KiB 48 KiB 48.0 45 KiB 45.0 41 KiB 41.0
> 2 KiB 48 KiB 24.0 45 KiB 22.5 62 KiB 31.0
> 4 KiB 82 KiB 20.5 80 KiB 20.0 73 KiB 18.3
> 8 KiB 121 KiB 15.1 90 KiB 11.3 89 KiB 11.1
> 16 KiB 217 KiB 13.6 146 KiB 9.1 113 KiB 7.1
> 32 KiB 506 KiB 15.8 314 KiB 9.8 158 KiB 4.9
> 64 KiB 1472 KiB 23.0 826 KiB 12.9 259 KiB 4.0
> 128 KiB 5585 KiB 43.6 3765 KiB 29.4 452 KiB 3.5
> 256 KiB 20424 KiB 79.8 10743 KiB 42.0 2351 KiB 9.2
> 512 KiB 86715 KiB 169.4 43650 KiB 85.3 3204 KiB 6.3
> 1024 KiB 369568 KiB 360.9 187496 KiB 183.1 15845 KiB 15.5
>
> Since `file_set_contents` also performs a `rename` after writing, the
> following table shows the results when the file is written without
> renaming it afterwards:
>
> print big_writes+print big_writes+syswrite
> file size written amplif. written amplif. written amplif.
> 1 KiB 29 KiB 29.0 29 KiB 29.0 25 KiB 25.0
> 2 KiB 29 KiB 14.5 30 KiB 15.0 25 KiB 12.5
> 4 KiB 37 KiB 9.3 44 KiB 11.0 41 KiB 10.3
> 8 KiB 61 KiB 7.6 45 KiB 5.6 45 KiB 5.6
> 16 KiB 143 KiB 8.9 86 KiB 5.4 57 KiB 3.6
> 32 KiB 396 KiB 12.4 225 KiB 7.0 69 KiB 2.2
> 64 KiB 1281 KiB 20.0 673 KiB 10.5 105 KiB 1.6
> 128 KiB 4789 KiB 37.4 3478 KiB 27.2 169 KiB 1.3
> 256 KiB 18868 KiB 73.7 9976 KiB 39.0 572 KiB 2.2
> 512 KiB 79304 KiB 154.9 42714 KiB 83.4 2150 KiB 4.2
> 1024 KiB 347929 KiB 339.8 182483 KiB 178.2 11133 KiB 10.9
>
> [1] https://lists.proxmox.com/pipermail/pve-devel/2024-September/065396.html
>
> Signed-off-by: Filip Schauer <f.schauer@proxmox.com>
> ---
> Changes since v1:
> * Add benchmark results without rename to commit message
> * Fix "Wide character in syswrite" error by first encoding $data with print
>
> src/PVE/Tools.pm | 21 ++++++++++++++++++---
> 1 file changed, 18 insertions(+), 3 deletions(-)
>
>
applied, and many thanks for the detailed benchmarks!
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next prev parent reply other threads:[~2024-10-14 8:42 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-30 11:40 [pve-devel] " Filip Schauer
2024-10-14 8:42 ` Thomas Lamprecht [this message]
2024-10-14 9:07 ` [pve-devel] applied: " Dominik Csapak
2024-10-14 9:22 ` Thomas Lamprecht
2024-10-14 9:26 ` [pve-devel] " Thomas Lamprecht
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