netdev - Re: [PATCH v4 net-next] hv_netvsc: Add per-cpu ethtool stats for netvsc

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Message-ID: <20180730103406.189cdc5d@xeon-e3>
Date:   Mon, 30 Jul 2018 10:34:06 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Yidong Ren <yidren@...uxonhyperv.com>
Cc:     Yidong Ren <yidren@...rosoft.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "David S. Miller" <davem@...emloft.net>,
        devel@...uxdriverproject.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, madhans@...rosoft.com
Subject: Re: [PATCH v4 net-next] hv_netvsc: Add per-cpu ethtool stats for
 netvsc

On Mon, 30 Jul 2018 17:09:45 +0000
Yidong Ren <yidren@...uxonhyperv.com> wrote:

> From: Yidong Ren <yidren@...rosoft.com>
> 
> This patch implements following ethtool stats fields for netvsc:
> cpu<n>_tx/rx_packets/bytes
> cpu<n>_vf_tx/rx_packets/bytes
> 
> Corresponding per-cpu counters already exist in current code. Exposing
> these counters will help troubleshooting performance issues.
> 
> for_each_present_cpu() was used instead of for_each_possible_cpu().
> for_each_possible_cpu() would create very long and useless output.
> It is still being used for internal buffer, but not for ethtool
> output.
> 
> There could be an overflow if cpu was added between ethtool
> call netvsc_get_sset_count() and netvsc_get_ethtool_stats() and
> netvsc_get_strings(). (still safe if cpu was removed)
> ethtool makes these three function calls separately.
> As long as we use ethtool, I can't see any clean solution.
> 
> Currently and in foreseeable short term, Hyper-V doesn't support
> cpu hot-plug. Plus, ethtool is for admin use. Unlikely the admin
> would perform such combo operations.
> 
> Signed-off-by: Yidong Ren <yidren@...rosoft.com>

Reviewed-by: Stephen Hemminger <sthemmin@...rosoft.com>