From: Stefan Sperling <stsp@stsp.name>
Subject: Re: Remove unnecessary context switches
To: Martin Pieuchot <mpi@openbsd.org>
Cc: gameoftrees@openbsd.org
Date: Sun, 19 Jan 2020 14:17:36 +0100

On Sun, Jan 19, 2020 at 01:46:16PM +0100, Martin Pieuchot wrote:
> tog(1) calls pthread_yield(3) without good reason.  This function
> commonly indicates a better synchronisation primitive is required.
> However in the two places below this isn't the case.  Removing those
> calls makes the tool faster in my small tests.
> 
> I'd appreciate more tests to be sure there's no regression.
> 
> Ok?

Sure. I don't see a downside and it still works.

> diff --git tog/tog.c tog/tog.c
> index c1f1819..db59543 100644
> --- tog/tog.c
> +++ tog/tog.c
> @@ -739,15 +739,6 @@ view_input(struct tog_view **new, struct tog_view **dead,
>  	*focus = NULL;
>  
>  	if (view->searching && !view->search_next_done) {
> -		errcode = pthread_mutex_unlock(&tog_mutex);
> -		if (errcode)
> -			return got_error_set_errno(errcode,
> -			    "pthread_mutex_unlock");
> -		pthread_yield();
> -		errcode = pthread_mutex_lock(&tog_mutex);
> -		if (errcode)
> -			return got_error_set_errno(errcode,
> -			    "pthread_mutex_lock");
>  		view->search_next(view);
>  		return NULL;
>  	}
> @@ -1652,16 +1643,6 @@ trigger_log_thread(int load_all, int *commits_needed, int *log_complete,
>  		if (errcode)
>  			return got_error_set_errno(errcode,
>  			    "pthread_cond_signal");
> -		errcode = pthread_mutex_unlock(&tog_mutex);
> -		if (errcode)
> -			return got_error_set_errno(errcode,
> -			    "pthread_mutex_unlock");
> -		pthread_yield();
> -		errcode = pthread_mutex_lock(&tog_mutex);
> -		if (errcode)
> -			return got_error_set_errno(errcode,
> -			    "pthread_mutex_lock");
> -
>  		if (*commits_needed > 0 && (!load_all || --max_wait <= 0)) {
>  			/*
>  			 * Thread is not done yet; lose a key press
> 
>