linux-kernel - Re: [GIT PULL] RCU changes for v4.1

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Message-ID: <CA+55aFz2sOTesK9ubr8Ds1SO9TxoUC37qP1opJvRofGNMZU4tg@mail.gmail.com>
Date:	Tue, 14 Apr 2015 20:19:57 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] RCU changes for v4.1

On Tue, Apr 14, 2015 at 7:55 PM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
>
> Does the (currently being tested) patch below fix things up?  If not,
> please fill me in on the further error of my ways.

Looks ok.

That said, couldn't that last dummy gp_init_delay variable:

> +/* Delay in jiffies for grace-period initialization delays, debug only. */
> +#ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT
> +static int gp_init_delay = CONFIG_RCU_TORTURE_TEST_SLOW_INIT_DELAY;
>  module_param(gp_init_delay, int, 0644);
> +#else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */
> +static const int gp_init_delay;
> +#endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */

be just a

  #define gp_init_delay 0

for the non-CONFIG_RCU_TORTURE_TEST_SLOW_INIT case, so that the code
that then does

+               if (gp_init_delay > 0 &&
+                   !(rsp->gpnum % (rcu_num_nodes * PER_RCU_NODE_PERIOD)))

would just trivially compile away.

I guess the compiler *might* see a 'static const int' that is never
touched and realize it's always zero, but it's not obvious that will
be the case.

                       Linus

                       Linus
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