netdev - Re: [PATCH net-next] tcp: force a PSH flag on TSO packets

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Message-ID: <cd1cce3d-faf5-d35b-7fd4-a831561eea14@gmail.com>
Date:   Thu, 19 Sep 2019 06:46:01 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Or Gerlitz <gerlitz.or@...il.com>,
        Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [PATCH net-next] tcp: force a PSH flag on TSO packets



On 9/19/19 5:17 AM, Or Gerlitz wrote:
> On Wed, Sep 11, 2019 at 12:54 AM Eric Dumazet <edumazet@...gle.com> wrote:
>> When tcp sends a TSO packet, adding a PSH flag on it
>> reduces the sojourn time of GRO packet in GRO receivers.
>>
>> This is particularly the case under pressure, since RX queues
>> receive packets for many concurrent flows.
>>
>> A sender can give a hint to GRO engines when it is
>> appropriate to flush a super-packet, especially when pacing
> 
> Hi Eric,
> 
> Is this correct that we add here the push flag for the tcp header template
> from which all the tcp headers for SW GSO packets will be generated?
> 
> Wouldn't that cause a too early flush on GRO engines at the receiver side?


If a TSO engine is buggy enough to add the PSH on all the segments, it needs
to be fixed urgently :)