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Message-ID: <92768fc4-4fe0-f74a-d61c-dde0eb64e2c0@huawei.com>
Date: Tue, 3 Dec 2024 21:10:17 +0800
From: zuoze <zuoze1@...wei.com>
To: Uladzislau Rezki <urezki@...il.com>
CC: Matthew Wilcox <willy@...radead.org>, <gustavoars@...nel.org>,
<akpm@...ux-foundation.org>, <linux-hardening@...r.kernel.org>,
<linux-mm@...ck.org>, <keescook@...omium.org>, <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH -next] mm: usercopy: add a debugfs interface to bypass the
vmalloc check.
在 2024/12/3 20:39, Uladzislau Rezki 写道:
> On Tue, Dec 03, 2024 at 07:23:44PM +0800, zuoze wrote:
>> We have implemented host-guest communication based on the TUN device
>> using XSK[1]. The hardware is a Kunpeng 920 machine (ARM architecture),
>> and the operating system is based on the 6.6 LTS version with kernel
>> version 6.6. The specific stack for hotspot collection is as follows:
>>
>> - 100.00% 0.00% vhost-12384 [unknown] [k] 0000000000000000
>> - ret_from_fork
>> - 99.99% vhost_task_fn
>> - 99.98% 0xffffdc59f619876c
>> - 98.99% handle_rx_kick
>> - 98.94% handle_rx
>> - 94.92% tun_recvmsg
>> - 94.76% tun_do_read
>> - 94.62% tun_put_user_xdp_zc
>> - 63.53% __check_object_size
>> - 63.49% __check_object_size.part.0
>> find_vmap_area
>> - 30.02% _copy_to_iter
>> __arch_copy_to_user
>> - 2.27% get_rx_bufs
>> - 2.12% vhost_get_vq_desc
>> 1.49% __arch_copy_from_user
>> - 0.89% peek_head_len
>> 0.54% xsk_tx_peek_desc
>> - 0.68% vhost_add_used_and_signal_n
>> - 0.53% eventfd_signal
>> eventfd_signal_mask
>> - 0.94% handle_tx_kick
>> - 0.94% handle_tx
>> - handle_tx_copy
>> - 0.59% vhost_tx_batch.constprop.0
>> 0.52% tun_sendmsg
>>
>> It can be observed that most of the overhead is concentrated in the
>> find_vmap_area function.
>>
> I see. Yes, it is pretty contented, since you run the v6.6 kernel. There
> was a work that tends to improve it to mitigate a vmap lock contention.
> See it here: https://lwn.net/Articles/956590/
>
> The work was taken in the v6.9 kernel:
>
> <snip>
> commit 38f6b9af04c4b79f81b3c2a0f76d1de94b78d7bc
> Author: Uladzislau Rezki (Sony) <urezki@...il.com>
> Date: Tue Jan 2 19:46:23 2024 +0100
>
> mm: vmalloc: add va_alloc() helper
>
> Patch series "Mitigate a vmap lock contention", v3.
>
> 1. Motivation
> ...
> <snip>
>
> Could you please try the v6.9 kernel on your setup?
>
> How to solve it, probably, it can be back-ported to the v6.6 kernel.
All the vmalloc-related optimizations have already been merged into 6.6,
including the set of optimization patches you suggested. Thank you very
much for your input.
>
> Thanks!
>
> --
> Uladzislau Rezki
>
Thanks,
ze zuo
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