netdev - RE: [PATCH V1 net 2/2] net: ena: fix too long default tx interrupt moderation interval

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Date:   Wed, 6 Nov 2019 19:13:06 +0000
From:   "Kiyanovski, Arthur" <akiyano@...zon.com>
To:     David Miller <davem@...emloft.net>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        "Machulsky, Zorik" <zorik@...zon.com>,
        "Matushevsky, Alexander" <matua@...zon.com>,
        "Bshara, Saeed" <saeedb@...zon.com>,
        "Wilson, Matt" <msw@...zon.com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        "Bshara, Nafea" <nafea@...zon.com>,
        "Tzalik, Guy" <gtzalik@...zon.com>,
        "Belgazal, Netanel" <netanel@...zon.com>,
        "Saidi, Ali" <alisaidi@...zon.com>,
        "Herrenschmidt, Benjamin" <benh@...zon.com>,
        "Dagan, Noam" <ndagan@...zon.com>,
        "Agroskin, Shay" <shayagr@...zon.com>,
        "Jubran, Samih" <sameehj@...zon.com>
Subject: RE: [PATCH V1 net 2/2] net: ena: fix too long default tx interrupt
 moderation interval



> -----Original Message-----
> From: David Miller <davem@...emloft.net>
> Sent: Monday, November 4, 2019 9:19 PM
> To: Kiyanovski, Arthur <akiyano@...zon.com>
> Cc: netdev@...r.kernel.org; Woodhouse, David <dwmw@...zon.co.uk>;
> Machulsky, Zorik <zorik@...zon.com>; Matushevsky, Alexander
> <matua@...zon.com>; Bshara, Saeed <saeedb@...zon.com>; Wilson,
> Matt <msw@...zon.com>; Liguori, Anthony <aliguori@...zon.com>;
> Bshara, Nafea <nafea@...zon.com>; Tzalik, Guy <gtzalik@...zon.com>;
> Belgazal, Netanel <netanel@...zon.com>; Saidi, Ali
> <alisaidi@...zon.com>; Herrenschmidt, Benjamin <benh@...zon.com>;
> Dagan, Noam <ndagan@...zon.com>; Agroskin, Shay
> <shayagr@...zon.com>
> Subject: Re: [PATCH V1 net 2/2] net: ena: fix too long default tx interrupt
> moderation interval
> 
> From: <akiyano@...zon.com>
> Date: Mon, 4 Nov 2019 13:58:48 +0200
> 
> > From: Arthur Kiyanovski <akiyano@...zon.com>
> >
> > Current default non-adaptive tx interrupt moderation interval is 196 us.
> > This commit sets it to 0, which is much more sensible as a default value.
> > It can be modified using ethtool -C.
> >
> > Signed-off-by: Arthur Kiyanovski <akiyano@...zon.com>
> 
> I do not agree that turning TX interrupt moderation off completely is a more
> sensible default value.
> 
> Maybe a much smaller value, but turning off the coalescing delay completely
> is a bit much.

David,
Up until now, the ENA device did not support interrupt moderation, so effectively the default tx interrupt moderation interval was 0.
You are probably right that 0 is not an optimal value.
However until we research and find such an optimal value, in order to avoid a degradation in default performance, we want the default value in the new driver to be (effectively) the same as in the old driver.