Re: [dpdk-dev] [PATCH] examples/timer: fix incorrect time interval

[Thomas Monjalon <thomas@monjalon.net>]

15/04/2021 09:12, Min Hu (Connor):
> From: Chengchang Tang <tangchengchang@huawei.com>
> 
> Timer sample example assumes that the frequency of the timer is about
> 2Ghz to control the period of calling rte_timer_manage(). But this
> assumption is easy to fail. For example. the frequency of tsc on ARM64
> is much less than 2Ghz.
> 
> This patch uses the frequency of the current timer to calculate the
> correct time interval to ensure consistent result on all platforms.
> 
> In addition, the rte_rdtsc() is replaced with the more recommended
> rte_get_timer_cycles function in this patch.
> 
> Fixes: af75078fece3 ("first public release")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
> Signed-off-by: Min Hu (Connor) <humin29@huawei.com>
[...]
>  		/*
> -		 * Call the timer handler on each core: as we don't
> -		 * need a very precise timer, so only call
> -		 * rte_timer_manage() every ~10ms (at 2Ghz). In a real
> -		 * application, this will enhance performances as
> -		 * reading the HPET timer is not efficient.
> +		 * Call the timer handler on each core: as we don't need a
> +		 * very precise timer, so only call rte_timer_manage()
> +		 * every ~10ms. since rte_eal_hpet_init() has not been
> +		 * called, the rte_rdtsc() will be used at runtime.

I don't understand this last sentence.

> +		 * In a real application, this will enhance performances
> +		 * as reading the HPET timer is not efficient.
>  		 */
> -		cur_tsc = rte_rdtsc();
> +		cur_tsc = rte_get_timer_cycles();