Messages in this thread | | | Date | Tue, 10 Apr 2018 14:07:32 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH] time: tick-sched: use bool for tick_stopped |
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On Tue, 10 Apr 2018, Peter Zijlstra wrote:
> On Tue, Apr 10, 2018 at 06:07:17PM +0800, yuankuiz@codeaurora.org wrote: > > > > > > @@ -48,8 +48,8 @@ struct tick_sched { > > > > > > unsigned long check_clocks; > > > > > > enum tick_nohz_mode nohz_mode; > > > > > > > > > > > > + bool tick_stopped : 1; > > > > > > unsigned int inidle : 1; > > > > > > - unsigned int tick_stopped : 1; > > > > > > unsigned int idle_active : 1; > > > > > > unsigned int do_timer_last : 1; > > > > > > unsigned int got_idle_tick : 1; > > > > > > > > > > I don't think this is a good idea at all. > > > > > > > > > > Please see https://lkml.org/lkml/2017/11/21/384 for example. > > > > [ZJ] Thanks for this sharing. Looks like, this patch fall into the > > > > case of > > > > "Maybe". > > > > > > This patch falls into the case 'pointless' because it adds extra storage > > [ZJ] 1 bit vs 1 bit. no more. > > Since its a different type, the bitfields will not be merged. Also I'm > surprised a bitfield with base-type _Bool is even allowed. > > > > for no benefit at all. > > [ZJ] tick_stopped is returned by the tick_nohz_tick_stopped() which is bool. > > The benefit is no any potiential type conversion could be minded. > > Do you have any actual evidence for that? Is there a compiler stupid > enough to generate code to convert a bool to a 1bit value?
Sure, if you do:
> > > > > > + bool tick_stopped : 1;
which is stupidly allowed by the standard....
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