Re: [Tarantool-patches] [PATCH v2 1/2] fiber: reset clock stats on fiber.top_enable()

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

Hi! Thanks for the fixes!

See 2 comments below.

On 15/11/2019 15:58, Serge Petrenko wrote:
> We didn't refresh last remembered clock on fiber.top_enable()
> This means that the fiber issuing fiber.top_enable() would get a huge
> chunk of cpu time on its first yield. Fix this.
> Also reset clock_delta and cpu_miss_count.
> 
> If fiber.top() is issued on the same ev loop iteration as
> fiber.top_enable(), clock_delta_last is 0 for both cord and all the
> fibers, so report "instant" and "average" stats per last iteration as 0
> instead of NaN.
> 
> Follow-up #2694
> ---
>  src/lib/core/fiber.c | 21 +++++++++++++++++++++
>  src/lua/fiber.c      | 12 ++++++++++--
>  2 files changed, 31 insertions(+), 2 deletions(-)
> 
> diff --git a/src/lib/core/fiber.c b/src/lib/core/fiber.c
> index aebaba7f0..258c094f5 100644
> --- a/src/lib/core/fiber.c
> +++ b/src/lib/core/fiber.c
> @@ -1203,9 +1203,30 @@ fiber_top_enable()
>  		ev_check_start(cord()->loop, &cord()->check_event);
>  		fiber_top_enabled = true;
>  
> +		/*
> +		 * Reset cord and fiber clock stats in order to
> +		 * count from zero even on reenable.
> +		 */
>  		cord()->clock_acc = 0;
>  		cord()->cpu_miss_count_last = 0;
>  		cord()->clock_delta_last = 0;
> +		cord()->clock_delta = 0;
> +
> +		struct fiber * fiber;
> +		rlist_foreach_entry(fiber, &cord()->alive, link) {
> +			fiber->clock_acc = 0;
> +			fiber->clock_delta_last = 0;
> +			fiber->clock_delta = 0;
> +			fiber->cputime = 0;

1. fiber_reset() should do exactly the same, right?
Then why doesn't it nullify clock_delta_last?

This mess with numerous time fields, and their reset,
looks like a necessity to create a new structure,
which would be included into cord and fiber structures.
And which would provide methods for cleaning and
updating the members.

> +		}
> +
> +		cord()->sched.clock_acc = 0;
> +		cord()->sched.clock_delta_last = 0;
> +		cord()->sched.clock_delta = 0;
> +		cord()->sched.cputime = 0;
> +
> +		cord()->clock_last = __rdtscp(&cord()->cpu_id_last);
> +		cord()->cpu_miss_count = 0;
>  		struct timespec ts;
>  		if (clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts) != 0) {
>  			say_debug("clock_gettime(): failed to get this"
> diff --git a/src/lua/fiber.c b/src/lua/fiber.c
> index 8b3b22e55..647505643 100644
> --- a/src/lua/fiber.c
> +++ b/src/lua/fiber.c
> @@ -335,11 +335,19 @@ lbox_fiber_top_entry(struct fiber *f, void *cb_ctx)
>  	lua_newtable(L);
>  
>  	lua_pushliteral(L, "average");
> -	lua_pushnumber(L, f->clock_acc / (double)cord()->clock_acc * 100);
> +	if (cord()->clock_acc)

2. Sorry for a nit, we usually compare with 0
explicitly, '!= 0', and avoid implicit casts.

> +		lua_pushnumber(L, f->clock_acc / (double)cord()->clock_acc * 100);
> +	else
> +		lua_pushnumber(L, 0);
>  	lua_settable(L, -3);
> +
>  	lua_pushliteral(L, "instant");
> -	lua_pushnumber(L, f->clock_delta_last / (double)cord()->clock_delta_last * 100);
> +	if (cord()->clock_delta_last)
> +		lua_pushnumber(L, f->clock_delta_last / (double)cord()->clock_delta_last * 100);
> +	else
> +		lua_pushnumber(L, 0);
>  	lua_settable(L, -3);
> +
>  	lua_pushliteral(L, "time");
>  	lua_pushnumber(L, f->cputime / (double) FIBER_TIME_RES);
>  	lua_settable(L, -3);
>