netdev - Re: [PATCH net-next] r8169: Add 64bit statistics

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Message-ID: <CABoNC83U2k=-6-BkJEyWBXfSnEbb-+K8CD1ffqhjA613Tk04tQ@mail.gmail.com>
Date:	Thu, 17 Nov 2011 18:59:57 +0800
From:	Junchang Wang <junchangwang@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Stephen Hemminger <stephen.hemminger@...tta.com>,
	netdev@...r.kernel.org, romieu@...zoreil.com,
	nic swsd <nic_swsd@...ltek.com>
Subject: Re: [PATCH net-next] r8169: Add 64bit statistics

> Yes, look at sky2.c for a template
>
> drivers/net/ethernet/marvell/sky2.c contains code like that
> (different syncp for rx/tx)
>
> TX path:
>                        u64_stats_update_begin(&sky2->tx_stats.syncp);
>                        ++sky2->tx_stats.packets;
>                        sky2->tx_stats.bytes += skb->len;
>                        u64_stats_update_end(&sky2->tx_stats.syncp);
>
>
> RX path:
>
>        u64_stats_update_begin(&sky2->rx_stats.syncp);
>        sky2->rx_stats.packets += packets;
>        sky2->rx_stats.bytes += bytes;
>        u64_stats_update_end(&sky2->rx_stats.syncp);
>

Thanks, Eric.

I'm still confused about why we need two sync entries. Please correct
me if I'm wrong.

Take r8169 for example, All statistic entries are updated in
rtl8169_rx_interrupt() or rtl8169_tx_interrupt(). Those two functions
are called in rtl8169_poll().
As far as I know, rtl8169_poll() is protected by NAPI_STATE_SCHED bit
to run on a single core at one moment. So there is not compulsory to
use two sync entries.

One benefit from two sync is that readers can avoid many retries.

Thanks.
-- 
--Junchang
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