netdev - Re: 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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Date:	Thu, 8 May 2014 00:18:32 +0800
From:	V JobNickname <workofv@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Netdev <netdev@...r.kernel.org>
Subject: Re: Is 3.18 patch "The tcp: TSO packets automatic sizing" will cause
 to Troughput drop when enable NO_HZ_IDEL or HIGH_RES_TIMERS ?

Try to lower
#define STMMAC_COAL_TX_TIMER    10000
or
#define STMMAC_TX_FRAMES    0 (this will casue to skip coalescing path)
can't solve the issue.

2014-05-07 23:45 GMT+08:00 Eric Dumazet <eric.dumazet@...il.com>:
> On Wed, 2014-05-07 at 22:27 +0800, V JobNickname wrote:
>> 2014-05-07 0:41 GMT+08:00 Eric Dumazet <eric.dumazet@...il.com>:
>> > On Tue, 2014-05-06 at 09:30 -0700, Eric Dumazet wrote:
>> >
>> >> I cant see any effect for this patch explaining a 50% reduction in
>> >> speed, unless a special qdisc setup maybe.
>> >
>> > Oh wait, a buggy driver could explain the problem.
>> >
>> > Some drivers really expected TX completion to happen as a side effect of
>> > subsequent transmits.
>> >
>> > You'll have to give more details on the configuration you are using.
>> >
>> >
>> >
>> Does the "buggy driver" here mean the NIC driver or some higher level
>> network stack driver?
>> The xmit function of the used NIC driver is to stuff DMA channel, is
>> there have "expected Tx completion" behavior in the driver's flow ?
>>
>> The more detail:
>>
>> 1. The platform's NIC is compilable with dwmac, use driver
>> ethernet/stmicro/stmmac
>>      some feature controls in plat_stmmacenet_data are set as
>>         .phy_bus_name = "stmmac",
>>         .bus_id = 0,
>>         .phy_addr = -1, /*auto phy by pooling by mdio bus */
>>         .has_gmac = 1,
>>         .enh_desc = 0,
>>         .tx_coe = 1,
>>         .rx_coe = STMMAC_RX_COE_TYPE2,
>
> Right, this driver seems to implement a 'coalescing tx strategy' using a
> 40ms timer.
>
> Try to lower STMMAC_COAL_TX_TIMER ?
>
>
>
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