netdev - Re: [PATCH v1] timer:clock:ptp: add support the dynamic posix clock alarm set for ptp

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Date:   Tue, 7 May 2019 06:49:52 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Po Liu <po.liu@....com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "Y.b. Lu" <yangbo.lu@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Leo Li <leoyang.li@....com>, Roy Zang <roy.zang@....com>,
        Mingkai Hu <mingkai.hu@....com>,
        "deepa.kernel@...il.com" <deepa.kernel@...il.com>
Subject: Re: [PATCH v1] timer:clock:ptp: add support the dynamic posix clock
 alarm set for ptp

On Sun, May 05, 2019 at 05:02:05AM +0000, Po Liu wrote:
> Current kernel code do not support the dynamic posix clock alarm set.
> This code would support it by the posix timer structure.
> 
> 319  const struct k_clock clock_posix_dynamic = {
> 
> 320         .clock_getres   = pc_clock_getres,
> 321         .clock_set      = pc_clock_settime,
> 322         .clock_get      = pc_clock_gettime,
> 323         .clock_adj      = pc_clock_adjtime,
> 324 +       .timer_create   = pc_timer_create,
> 325 +       .timer_del      = pc_timer_delete,
> 326 +       .timer_set      = pc_timer_set,
> 327 +       .timer_arm      = pc_timer_arm,
> }
> 

Sorry, NAK, since we decided some time ago not to support timer_*
operations on dynamic clocks.  You get much better application level
timer performance by synchronizing CLOCK_REALTIME to your PHC and
using clock_nanosleep() with CLOCK_REALTIME or CLOCK_MONOTONIC.

> This won't change the user space system call code. Normally the user
> space set alarm by timer_create() and timer_settime(). Reference code
> are tools/testing/selftests/ptp/testptp.c.

That program still has misleading examples.  Sorry about that.  I'll
submit a patch to remove them.

> +static int pc_timer_create(struct k_itimer *new_timer)
> +{
> +	return 0;
> +}
> +

This of course would never work.  Consider what happens when two or
more timers are created and armed.

Thanks,
Richard