netdev - Re: [RFC PATCH 01/13] net: dsa: add plumbing for custom netdev statistics

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Message-ID: <20201018173649.GF456889@lunn.ch>
Date:   Sun, 18 Oct 2020 19:36:49 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org,
        f.fainelli@...il.com, vivien.didelot@...il.com,
        Christian Eggers <ceggers@...i.de>,
        Kurt Kanzenbach <kurt@...utronix.de>
Subject: Re: [RFC PATCH 01/13] net: dsa: add plumbing for custom netdev
 statistics

On Sun, Oct 18, 2020 at 09:49:51AM -0700, Jakub Kicinski wrote:
> > +	struct u64_stats_sync	syncp;
> > +} __aligned(1 * sizeof(u64));
> 
> Why aligned to u64? Compiler should pick a reasonable alignment here 
> by itself.

Hi Jakub

I wondered that as well. But:

struct gnet_stats_basic_cpu {
        struct gnet_stats_basic_packed bstats;
        struct u64_stats_sync syncp;
} __aligned(2 * sizeof(u64));

/* often modified stats are per-CPU, other are shared (netdev->stats) */
struct pcpu_sw_netstats {
        u64     rx_packets;
        u64     rx_bytes;
        u64     tx_packets;
        u64     tx_bytes;
        struct u64_stats_sync   syncp;
} __aligned(4 * sizeof(u64));

struct pcpu_lstats {
        u64_stats_t packets;
        u64_stats_t bytes;
        struct u64_stats_sync syncp;
} __aligned(2 * sizeof(u64));

Cargo cult or is there a real need?

      Andrew