From: Vadim Fedorenko <vadim.fedorenko@linux•dev>
To: Willem de Bruijn <willemdebruijn.kernel@gmail•com>,
Vadim Fedorenko <vadfed@meta•com>,
Jakub Kicinski <kuba@kernel•org>,
Willem de Bruijn <willemb@google•com>,
Paolo Abeni <pabeni@redhat•com>, David Ahern <dsahern@kernel•org>
Cc: netdev@vger•kernel.org
Subject: Re: [RFC PATCH] net_tstamp: add SCM_TS_OPT_ID to provide OPT_ID in control message
Date: Thu, 29 Aug 2024 16:00:21 +0100 [thread overview]
Message-ID: <f5e46e19-b045-4ac8-b871-32affe3202c0@linux.dev> (raw)
In-Reply-To: <66d0856b4234a_38c94929436@willemb.c.googlers.com.notmuch>
On 29/08/2024 15:27, Willem de Bruijn wrote:
> Vadim Fedorenko wrote:
>> On 29/08/2024 14:31, Willem de Bruijn wrote:
>>> Vadim Fedorenko wrote:
>>>> SOF_TIMESTAMPING_OPT_ID socket option flag gives a way to correlate TX
>>>> timestamps
>>>
>>> +1 on the feature. Few minor points only.
>>>
>>> Not a hard requirement, but would be nice if there was a test,
>>> e.g., as a tools/testing/../txtimestamp.c extension.
>>
>> Sure, I'll add some tests in the next version.
>>
>>
>>>> and packets sent via socket. Unfortunately, there is no way
>>>> to reliably predict socket timestamp ID value in case of error returned
>>>> by sendmsg [1].
>>>
>>> Might be good to copy more context from the discussion to explain why
>>> reliable OPT_ID is infeasible. For UDP, it is as simple as lockless
>>> transmit. For RAW, things like MSG_MORE come into play.
>>
>> Ok, I'll add it, thanks!
>>
>>>> This patch adds new control message type to give user-space
>>>> software an opportunity to control the mapping between packets and
>>>> values by providing ID with each sendmsg. This works fine for UDP
>>>> sockets only, and explicit check is added to control message parser.
>>>> Also, there is no easy way to use 0 as provided ID, so this is value
>>>> treated as invalid.
>>>
>>> This is because the code branches on non-zero value in the cookie,
>>> else uses ts_key. Please make this explicit. Or perhaps better, add a
>>> bit in the cookie so that the full 32-bit space can be used.
>>
>> Adding a bit in the cookie is not enough, I have to add another flag to
>> inet_cork. And we are running out of space for tx flags,
>> inet_cork::tx_flags is u8 and we have only 1 bit left for SKBTX* enum.
>> Do you think it's OK to use this last bit for OPT_ID feature?
>
> No, that space is particularly constrained in skb_shinfo.
>
> Either a separate bit in inet_cork, or just keep as is.
Ok, got it. I'll add IPCORK_TS_OPT_ID flag then. Thanks!
prev parent reply other threads:[~2024-08-29 15:00 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-08-29 0:03 [RFC PATCH] net_tstamp: add SCM_TS_OPT_ID to provide OPT_ID in control message Vadim Fedorenko
2024-08-29 13:31 ` Willem de Bruijn
2024-08-29 14:13 ` Vadim Fedorenko
2024-08-29 14:27 ` Willem de Bruijn
2024-08-29 15:00 ` Vadim Fedorenko [this message]
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