linux-kernel - Re: [PATCH v3 1/3] rcutorture: Allow a negative value for nfakewriters

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Message-ID: <a26d4cc5-ff54-4f9f-b2df-aa423c112487@nvidia.com>
Date: Wed, 26 Feb 2025 12:49:41 -0500
From: Joel Fernandes <joelagnelf@...dia.com>
To: Uladzislau Rezki <urezki@...il.com>
Cc: "Paul E . McKenney" <paulmck@...nel.org>,
 Boqun Feng <boqun.feng@...il.com>, RCU <rcu@...r.kernel.org>,
 LKML <linux-kernel@...r.kernel.org>,
 Frederic Weisbecker <frederic@...nel.org>,
 Cheung Wall <zzqq0103.hey@...il.com>,
 Neeraj upadhyay <Neeraj.Upadhyay@....com>,
 Joel Fernandes <joel@...lfernandes.org>,
 Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH v3 1/3] rcutorture: Allow a negative value for
 nfakewriters



On 2/26/2025 9:29 AM, Uladzislau Rezki wrote:
> On Tue, Feb 25, 2025 at 04:24:09PM -0500, Joel Fernandes wrote:
>> On Tue, Feb 25, 2025 at 12:00:18PM +0100, Uladzislau Rezki (Sony) wrote:
>>> Currently "nfakewriters" parameter can be set to any value but
>>> there is no possibility to adjust it automatically based on how
>>> many CPUs a system has where a test is run on.
>>>
>>> To address this, if the "nfakewriters" is set to negative it will
>>> be adjusted to num_online_cpus() during torture initialization.
>>>
>>> Reviewed-by: Paul E. McKenney <paulmck@...nel.org>
>>> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
>>> ---
>>>  kernel/rcu/rcutorture.c | 22 ++++++++++++++++------
>>>  1 file changed, 16 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
>>> index d98b3bd6d91f..f376262532ce 100644
>>> --- a/kernel/rcu/rcutorture.c
>>> +++ b/kernel/rcu/rcutorture.c
>>> @@ -148,6 +148,7 @@ MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, srcu, ...)");
>>
>> IMO, this should also be updated to reflect the possibily to set it negative
>> and hence to number CPUs:
>>
>> torture_param(int, nfakewriters, 4, "Number of RCU fake writer threads");
>>
> You can set it to a negative as well as to number of CPUs or any other
> number.
Sorry I just meant amend the description to something like "Number of RCU fake
writer threads (or set to -1 for NR_CPUs)", so user does not have to read code
to know that (and update the kernel cmdline params document as well).

thanks,

 - Joel