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

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Date:   Sat, 3 Sep 2022 21:35:11 +0200
From:   Manfred Spraul <manfred@...orfullife.com>
To:     Jiebin Sun <jiebin.sun@...el.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
Subject: Re: [PATCH] ipc/msg.c: mitigate the lock contention with percpu
 counter

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.


> @@ -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.

--

     Manfred