netdev - Re: [PATCH net-next 0/2] net: sched: unify __gnet_stats_copy

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Message-ID: <f082962e-282f-f0dc-8773-b9107d39e482@linux.alibaba.com>
Date:   Mon, 23 Dec 2019 17:55:38 +0800
From:   Dust Li <dust.li@...ux.alibaba.com>
To:     David Miller <davem@...emloft.net>
Cc:     xiyou.wangcong@...il.com, jhs@...atatu.com,
        john.fastabend@...il.com, jiri@...nulli.us,
        tonylu@...ux.alibaba.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 0/2] net: sched: unify __gnet_stats_copy_xxx()
 for percpu and non-percpu


On 12/21/19 8:54 AM, David Miller wrote:
> From: Dust Li <dust.li@...ux.alibaba.com>
> Date: Tue, 17 Dec 2019 16:47:16 +0800
>
>> Currently, __gnet_stats_copy_xxx() will overwrite the return value when
>> percpu stats are not enabled. But when percpu stats are enabled, it will
>> add the percpu stats to the result. This inconsistency brings confusion to
>> its callers.
>>
>> This patch series unify the behaviour of __gnet_stats_copy_basic() and
>> __gnet_stats_copy_queue() for percpu and non-percpu stats and fix an
>> incorrect statistic for mqprio class.
>>
>> - Patch 1 unified __gnet_stats_copy_xxx() for both percpu and non-percpu
>> - Patch 2 depending on Patch 1, fixes the problem that 'tc class show'
>>    for mqprio class is always 0.
> I think this is going to break the estimator.
>
> The callers of est_fetch_counters() expect continually incrementing
> statistics.  It does relative subtractions from previous values each
> time, so if we just reset on the next statistics fetch it won't work.
>
> Sorry I can't apply this.


Hi David,

Thanks for your reply.


I checked the callers of est_fetch_counters(). I think there is a little
misunderstanding here.We memset() the 'gnet_stats_basic_packed *b'which
is not the original data of the estimator,but just the return value.
Actually, it has been already memseted in est_fetch_counters() now. So it
shouldnot break the estimator.

static void est_fetch_counters(struct net_rate_estimator *e,
                                struct gnet_stats_basic_packed *b)
{
/        memset(b, 0, sizeof(*b));     // <<--- Here b is already memseted/
         if (e->stats_lock)
                 spin_lock(e->stats_lock);

         __gnet_stats_copy_basic(e->running, b, e->cpu_bstats, e->bstats);

         if (e->stats_lock)
                 spin_unlock(e->stats_lock);

}


The purpose of this memset() is to maintain a consistent semantics for both
percpu and non-percpu statisticsin __gnet_stats_copy_basic().


Thanks

Dust