linux-kernel - Re: [PATCH] [RFC] rcu/tree: Reduce wake up for synchronize

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Message-ID: <a65bb5d1-8d44-44cd-ba45-d9549fbd870e@joelfernandes.org>
Date: Fri, 8 Mar 2024 19:46:38 -0500
From: Joel Fernandes <joel@...lfernandes.org>
To: paulmck@...nel.org, Uladzislau Rezki <urezki@...il.com>
Cc: linux-kernel@...r.kernel.org, frederic@...nel.org, boqun.feng@...il.com,
 neeraj.iitr10@...il.com, rcu@...r.kernel.org, rostedt@...dmis.org,
 Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
 Josh Triplett <josh@...htriplett.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Lai Jiangshan <jiangshanlai@...il.com>, Zqiang <qiang.zhang1211@...il.com>
Subject: Re: [PATCH] [RFC] rcu/tree: Reduce wake up for synchronize_rcu()
 common case



On 3/8/2024 4:52 PM, Paul E. McKenney wrote:
> On Fri, Mar 08, 2024 at 06:38:37PM +0100, Uladzislau Rezki wrote:
>> On Fri, Mar 08, 2024 at 04:05:15PM +0100, Uladzislau Rezki wrote:
>>> On Thu, Mar 07, 2024 at 04:06:06PM -0800, Paul E. McKenney wrote:
>>>> On Thu, Mar 07, 2024 at 06:52:14PM -0500, Joel Fernandes wrote:
>>>>> On Thu, Mar 7, 2024 at 6:48 PM Joel Fernandes (Google)
>>>>> <joel@...lfernandes.org> wrote:
>>>>>>
>>>>>> In the synchronize_rcu() common case, we will have less than
>>>>>> SR_MAX_USERS_WAKE_FROM_GP number of users per GP. Waking up the kworker
>>>>>> is pointless just to free the last injected wait head since at that point,
>>>>>> all the users have already been awakened.
>>>>>>
>>>>>> Introduce a new counter to track this and prevent the wakeup in the
>>>>>> common case.
>>>>>>
>>>>>> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
>>>>>> ---
>>>>>
>>>>> Forgot to mention, this is based on the latest RCU -dev branch and
>>>>> passes light rcutorture testing on all configs. Heavier rcutorture
>>>>> testing (60 minutes) was performed on TREE03.
>>>>
>>>> Very good, thank you!
>>>>
>>>> Uladzislau, could you please pull this into the next series you send?
>>>> I can then replace your commits in -rcu with the updated series.
>>>>
>>> Absolutely. I will go through it and send out the next version!
>>>
>>
>> Joel, i sent out the v6: [PATCH v6 0/6] Reduce synchronize_rcu() latency(v6)
>>
>> Could you please rework the patch on latest tip once the series i sent is
>> settled on Paul's dev?
> 
> It is there now.

Thanks, I rebased on it and sent a v2 (along with that other comment for the
hotplug race ;-)).

 - Joel