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Message-ID: <20241101105253.GG101007@linux.alibaba.com>
Date: Fri, 1 Nov 2024 18:52:53 +0800
From: Dust Li <dust.li@...ux.alibaba.com>
To: liqiang <liqiang64@...wei.com>, wenjia@...ux.ibm.com,
jaka@...ux.ibm.com, alibuda@...ux.alibaba.com,
tonylu@...ux.alibaba.com, guwen@...ux.alibaba.com
Cc: linux-s390@...r.kernel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, luanjianhai@...wei.com,
zhangxuzhou4@...wei.com, dengguangxing@...wei.com,
gaochao24@...wei.com, kuba@...nel.org
Subject: Re: [PATCH net-next] net/smc: Optimize the search method of reused
buf_desc
On 2024-11-01 16:23:42, liqiang wrote:
>We create a lock-less link list for the currently
>idle reusable smc_buf_desc.
>
>When the 'used' filed mark to 0, it is added to
>the lock-less linked list.
>
>When a new connection is established, a suitable
>element is obtained directly, which eliminates the
>need for traversal and search, and does not require
>locking resource.
>
>A lock-less linked list is a linked list that uses
>atomic operations to optimize the producer-consumer model.
>
>I didn't find a suitable public benchmark, so I tested the
>time-consuming comparison of this function under multiple
>connections based on redis-benchmark (test in smc loopback-ism mode):
I think you can run test wrk/nginx test with short-lived connection.
For example:
```
# client
wrk -H "Connection: close" http://$serverIp
# server
nginx
```
>
> 1. On the current version:
> [x.832733] smc_buf_get_slot cost:602 ns, walk 10 buf_descs
> [x.832860] smc_buf_get_slot cost:329 ns, walk 12 buf_descs
> [x.832999] smc_buf_get_slot cost:479 ns, walk 17 buf_descs
> [x.833157] smc_buf_get_slot cost:679 ns, walk 13 buf_descs
> ...
> [x.045240] smc_buf_get_slot cost:5528 ns, walk 196 buf_descs
> [x.045389] smc_buf_get_slot cost:4721 ns, walk 197 buf_descs
> [x.045537] smc_buf_get_slot cost:4075 ns, walk 198 buf_descs
> [x.046010] smc_buf_get_slot cost:6476 ns, walk 199 buf_descs
>
> 2. Apply this patch:
> [x.180857] smc_buf_get_slot_free cost:75 ns
> [x.181001] smc_buf_get_slot_free cost:147 ns
> [x.181128] smc_buf_get_slot_free cost:97 ns
> [x.181282] smc_buf_get_slot_free cost:132 ns
> [x.181451] smc_buf_get_slot_free cost:74 ns
>
>It can be seen from the data that it takes about 5~6us to traverse 200
>times, and the time complexity of the lock-less linked algorithm is O(1).
>
>And my test process is only single-threaded. If multiple threads
>establish SMC connections in parallel, locks will also become a
>bottleneck, and lock-less linked can solve this problem well.
>
>SO I guess this patch should be beneficial in scenarios where a
>large number of short connections are parallel?
Based on your data, I'm afraid the short-lived connection
test won't show much benificial. Since the time to complete a
SMC-R connection should be several orders of magnitude larger
than 100ns.
Best regards,
Dust
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