netdev - Re: [RFC PATCH v2 net-next 2/7] tcp: Merge tx_flags/tskey/txstamp_ack in tcp_collapse

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Message-ID: <CACSApvbzAtCTnom+xyQmaG=ATwncMnvLLDdxqCAYWG7rgYbBmw@mail.gmail.com>
Date:	Tue, 19 Apr 2016 14:24:38 -0400
From:	Soheil Hassas Yeganeh <soheil@...gle.com>
To:	Martin KaFai Lau <kafai@...com>
Cc:	Eric Dumazet <edumazet@...gle.com>,
	netdev <netdev@...r.kernel.org>,
	Neal Cardwell <ncardwell@...gle.com>,
	Soheil Hassas Yeganeh <soheil.kdev@...il.com>,
	Willem de Bruijn <willemb@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>,
	Kernel Team <kernel-team@...com>
Subject: Re: [RFC PATCH v2 net-next 2/7] tcp: Merge tx_flags/tskey/txstamp_ack
 in tcp_collapse_retrans

On Tue, Apr 19, 2016 at 2:18 PM, Martin KaFai Lau <kafai@...com> wrote:
> On Tue, Apr 19, 2016 at 10:35:52AM -0700, Eric Dumazet wrote:
>> On Tue, Apr 19, 2016 at 10:28 AM, Martin KaFai Lau <kafai@...com> wrote:
>>
>> > A bit off topic, I feel like the SKBTX_ACK_TSTAMP and txstamp_ack are sort
>> > of redundant but I have not look into the details yet, so not completely
>> > sure.  It wwould be a separate cleanup patch if it is the case.
>>
>> Please read 6b084928baac562ed61866f540a96120e9c9ddb7 changelog ;)
>>
>> A cache line miss avoidance is critical
> I looked at the patch but I probably am missing something :(
> Is checking txstamp_ack alone enough and SKBTX_ACK_TSTAMP is not needed
> since they are always set together?

That's right, the check on "(shinfo->tx_flags & SKBTX_ACK_TSTAMP)" in
tcp_ack_tstamp() is redundant and I had a patch prepared to remove it.
But I thought it's better to wait for
https://patchwork.ozlabs.org/patch/611938/ to be merged first.

Feel free to remove it in your patches, if you'd prefer that.