netdev - Re: [PATCH] tcp: Use BPF timeout setting for SYN ACK RTO

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Message-ID: <863fdf13-b1f4-f429-d8ac-269f9ceaa747@gmail.com>
Date:   Fri, 29 Oct 2021 09:30:15 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Akhmat Karakotov <hmukos@...dex-team.ru>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     Alexander Azimov <mitradir@...dex-team.ru>, zeil@...dex-team.ru,
        Lawrence Brakmo <brakmo@...com>, netdev@...r.kernel.org,
        Neal Cardwell <ncardwell@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH] tcp: Use BPF timeout setting for SYN ACK RTO



On 10/29/21 9:19 AM, Akhmat Karakotov wrote:
> 
>> On Oct 25, 2021, at 23:48, Eric Dumazet <eric.dumazet@...il.com> wrote:
>>
>> Also, have you checked if TCP syn cookies would still work
>> if tcp_timeout_init() returns a small value like 5ms ?
>>
>> tcp_check_req()
>> ...
>> tmp_opt.ts_recent_stamp = ktime_get_seconds() - ((tcp_timeout_init((struct sock *)req)/HZ)<<req->num_timeout);
>>
>> -> tmp_opt.ts_recent_stamp = ktime_get_seconds()
>>
>>
> 
> I may have overlooked this. As long as I remember TCP SYN cookies worked
> but I will recheck this place again. Also could you please tell in what way exactly
> does this relate to syn cookies? I may have misunderstood what the code does.
> 

This was badly written.

This should have been two different questions.