netdev - Is 3.18 patch "The tcp: TSO packets automatic sizing" will cause to Troughput drop when enable NO_HZ_IDEL or HIGH_RES

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Message-ID: <CANHbGWs=oQBDVVZc8h5wX0WY+PRbQfCqiv5FrF1tH29QGiRndA@mail.gmail.com>
Date:	Wed, 7 May 2014 00:17:43 +0800
From:	V JobNickname <workofv@...il.com>
To:	netdev@...r.kernel.org
Subject: Is 3.18 patch "The tcp: TSO packets automatic sizing" will cause to
 Troughput drop when enable NO_HZ_IDEL or HIGH_RES_TIMERS ?

When I porting my ARM platform to Kernel 3.10.0 the network throughput
of TCP tx is about 160 Mbps.

After I applied patch-3.10.37, the TCP tx drop to 8x Mbps.
I found that after I disabled CONFIG_HIGH_RES_TIMERS and NO_HZ_IDEL,
the throughput can back to 16x Mbps.

I try to find the more step patches and tile patch-3.10.17, the
throughput with enabled NO_HZ_IDEL or HIGH_RES_TIMERS can still have
16x Mbps
After applied patch-3.10.17-18, it start to drop the performance.

More detail trace, the first commit of 3.10.18, tcp: TSO packets
automatic sizing, cause to this issue.
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/diff/?id=5e25ba5003ee5de0ba2be56bfd54d16d4b1b028d

I don't know why this TSO patch affect my network since the network
driver doesn't enable NETIF_F_TSO.
But I
(dev->hw_features = NETIF_F_SG | NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM;
dev->features |= dev->hw_features;)

After look into the commit difference,
I can just doubt if function "tcp_update_pacing_rate" can work well
with NO_HZ_IDEL or HIGH_RES_TIMERS, since it base on jiffie to
calculate the rate instead of human nenosecond of new timer
arch(clocksource/clockevent)
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