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From:   Joel Fernandes <joel@joelfernandes.org>
Mime-Version: 1.0 (1.0)
Subject: Re: [PATCH] rcu: Make call_rcu() lazy only when CONFIG_RCU_LAZY is enabled
Date:   Wed, 19 Oct 2022 08:12:30 -0400
Message-Id: <F24713AB-9AC8-494F-A677-D52C9CE591CF@joelfernandes.org>
References: <B3E5FB1F-3184-4C56-8B11-6F422DBF1B53@joelfernandes.org>
Cc:     paulmck@kernel.org, frederic@kernel.org, rcu@vger.kernel.org,
        linux-kernel@vger.kernel.org
In-Reply-To: <B3E5FB1F-3184-4C56-8B11-6F422DBF1B53@joelfernandes.org>
To:     Zqiang <qiang1.zhang@intel.com>
Precedence: bulk


> On Oct 19, 2022, at 8:10 AM, Joel Fernandes <joel@joelfernandes.org> wrote=
:
>=20
> =EF=BB=BF
>=20
>> On Oct 19, 2022, at 6:34 AM, Zqiang <qiang1.zhang@intel.com> wrote:
>>=20
>> =EF=BB=BFCurrently, regardless of whether the CONFIG_RCU_LAZY is enabled,=

>> invoke the call_rcu() is always lazy, it also means that when
>> CONFIG_RCU_LAZY is disabled, invoke the call_rcu_flush() is also
>> lazy. therefore, this commit make call_rcu() lazy only when
>> CONFIG_RCU_LAZY is enabled.
>>=20
>> Signed-off-by: Zqiang <qiang1.zhang@intel.com>
>> ---
>> kernel/rcu/tree.c | 8 +++++++-
>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>=20
>> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
>> index abc615808b6e..97ef602da3d5 100644
>> --- a/kernel/rcu/tree.c
>> +++ b/kernel/rcu/tree.c
>> @@ -2839,7 +2839,6 @@ void call_rcu_flush(struct rcu_head *head, rcu_call=
back_t func)
>>   return __call_rcu_common(head, func, false);
>> }
>> EXPORT_SYMBOL_GPL(call_rcu_flush);
>> -#endif
>>=20
>> /**
>> * call_rcu() - Queue an RCU callback for invocation after a grace period.=

>> @@ -2890,6 +2889,13 @@ void call_rcu(struct rcu_head *head, rcu_callback_=
t func)
>>   return __call_rcu_common(head, func, true);
>> }
>> EXPORT_SYMBOL_GPL(call_rcu);
>> +#else
>> +void call_rcu(struct rcu_head *head, rcu_callback_t func)
>> +{
>> +    return __call_rcu_common(head, func, false);
>=20
> Thanks. Instead of adding new function, you can also pass IS_ENABLED(CONFI=
G=E2=80=A6) to the existing function of the same name.
>=20
> Looks like though I made every one test the patch without having to enable=
 the config option ;-). Hey, I=E2=80=99m a half glass full kind of guy, why d=
o you ask?
>=20
> Paul, I=E2=80=99ll take a closer look once I=E2=80=99m at the desk, but wo=
uld you prefer to squash a diff into the existing patch, or want a new patch=
 altogether?

On the other hand, what I=E2=80=99d want is to nuke the config option altoge=
ther or make it default y, we want to catch issues sooner than later.

Thanks.

>=20
> Thanks.
>=20
> - Joel
>=20
>=20
>> +}
>> +EXPORT_SYMBOL_GPL(call_rcu);
>> +#endif
>>=20
>> /* Maximum number of jiffies to wait before draining a batch. */
>> #define KFREE_DRAIN_JIFFIES (5 * HZ)
>> --=20
>> 2.25.1
>>=20