linux-kernel - Re: [PATCH] ipc/msg.c: mitigate the lock contention with percpu counter

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Message-ID: <f204eb92-d17d-9c6a-768c-5404f3363b5b@intel.com>
Date:   Mon, 5 Sep 2022 20:12:04 +0800
From:   "Sun, Jiebin" <jiebin.sun@...el.com>
To:     Manfred Spraul <manfred@...orfullife.com>,
        akpm@...ux-foundation.org, vasily.averin@...ux.dev,
        shakeelb@...gle.com, dennis@...nel.org, tj@...nel.org,
        cl@...ux.com, ebiederm@...ssion.com, legion@...nel.org,
        alexander.mikhalitsyn@...tuozzo.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     tim.c.chen@...el.com, feng.tang@...el.com, ying.huang@...el.com,
        tianyou.li@...el.com, wangyang.guo@...el.com, jiebin.sun@...el.com
Subject: Re: [PATCH] ipc/msg.c: mitigate the lock contention with percpu
 counter


On 9/4/2022 3:35 AM, Manfred Spraul wrote:
> Hi Jiebin,
>
> On 9/2/22 17:22, Jiebin Sun wrote:
>> The msg_bytes and msg_hdrs atomic counters are frequently
>> updated when IPC msg queue is in heavy use, causing heavy
>> cache bounce and overhead. Change them to percpu_counters
>> greatly improve the performance. Since there is one unique
>> ipc namespace, additional memory cost is minimal.
>
> With ipc namespaces, there is one struct per namespace, correct?
>
> The cost is probably still ok, but the change log should be correct.
>
Yes, that's what I want to summarize. The IPC msg namespace is unique

and there is only one percpu counter in IPC msg namespace.

Thanks.

>
>> @@ -1303,14 +1305,16 @@ void msg_init_ns(struct ipc_namespace *ns)
>>       ns->msg_ctlmnb = MSGMNB;
>>       ns->msg_ctlmni = MSGMNI;
>>   -    atomic_set(&ns->msg_bytes, 0);
>> -    atomic_set(&ns->msg_hdrs, 0);
>> +    percpu_counter_init(&ns->percpu_msg_bytes, 0, GFP_KERNEL);
>> +    percpu_counter_init(&ns->percpu_msg_hdrs, 0, GFP_KERNEL);
>>       ipc_init_ids(&ns->ids[IPC_MSG_IDS]);
>
> These calls can fail. You must add error handling.

I have add error handling for percpu_counter_init.

Thanks.

>
> -- 
>
>     Manfred
>
>