Re: [PATCH v2] Import a new test, jitterz

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2020-04-18 07:14:49 [-0700], trix@redhat.com wrote:
> --- /dev/null
> +++ b/src/jitterz/jitterz.c
> @@ -0,0 +1,400 @@
…
> +/*
> + * jitterz
> + *
> + * Copyright 2019-2020 Tom Rix <trix@redhat.com>
> + *
> + */
> +
> +#ifndef _GNU_SOURCE
> +#define _GNU_SOURCE
> +#endif

in general there is no need of that ifndef and this should be taken care
by the build system (and refuse the build if _GNU_SOURCE makes no
difference/ is not available). And then include the config.h (or so)
first header file. 
In rt-tests, the Makefile already adds this define to the CFLAGS.

…
> +/* Returns clock ticks */
> +static inline uint64_t time_stamp_counter(void)
> +{
> +	uint64_t ret = -1;
> +#if defined(__i386__) || defined(__x86_64__)
> +	uint32_t l, h;
> +
> +	__asm__ __volatile__("lfence");
> +	__asm__ __volatile__("rdtsc" : "=a"(l), "=d"(h));
> +	ret = ((uint64_t)h << 32) | l;
> +#else
> +	fprintf(stderr,
> +		"Add a time_stamp_counter function for your arch here %s:%d\n",
> +		__FILE__, __LINE__);
> +	exit(1);
> +#endif
> +	return ret;
> +}

I remember I complained about this in `queuelat' and it ended nowhere
once it got merged.
To repeat my question: Is there a reason not to use clock_gettime()?
With VDSO there should be hardly any difference between this and
clock_gettime().

Sebastian