netdev - Re: [PATCH][net-next] openvswitch: eliminate cpu_used_mask from sw

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Message-ID: <CAOrHB_DPY-yeq4BhyK-MXi1QB9h_omL4+hjop9JYGby7xm-+ew@mail.gmail.com>
Date:   Sat, 28 Jul 2018 12:05:40 -0700
From:   Pravin Shelar <pshelar@....org>
To:     Li RongQing <lirongqing@...du.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH][net-next] openvswitch: eliminate cpu_used_mask from sw_flow

On Fri, Jul 27, 2018 at 1:03 AM, Li RongQing <lirongqing@...du.com> wrote:
> The size of struct cpumask varies with CONFIG_NR_CPUS, some config
> CONFIG_NR_CPUS is very larger, like 5120, struct cpumask will take
> 640 bytes, if there is thousands of flows, it will take lots of
> memory
>
I am fine with removing cpumask bitmap from flow struct.

> cpu_used_mask has two purposes
> 1: Assume first cpu as cpu0 which maybe not true; now use
>    cpumask_first(cpu_possible_mask)

I am not sure about this, most of system would have cpu zero, so why
this change is done in this patch ? This adds overhead of calculating
first cpu when updating stats in fast path.

> 2: when get/clear statistic, reduce the iteratation; but it
>    is not hot path, so use for_each_possible_cpu
>