Re: Waiting for bufdaemon

On 1/20/21 11:18 AM, Konstantin Belousov wrote:
> On Wed, Jan 20, 2021 at 11:02:21AM +0100, Jakob Alvermark wrote:
>> This patch hides the problem for me. The system seems to work better now.
>>
>> No waiting on reboot, and the webcam works better.
> I am curious what do you mean by the above reference to webcam.
> Can you explain it with more details, even if only the impressions?
>
> I probably going to commit the following patch in the next 24 hours.
>
> commit 02505d07bca320a638c96918ac9076c6eece2fff
> Author: Konstantin Belousov <kib_at_FreeBSD.org>
> Date:   Wed Jan 20 11:32:21 2021 +0200
>
>      AMD Zen CPUs: switch TSC timecounter to RDTSCP
>      
>      Reported by:    many
>      MFC after:      1 weel
>      Sponsored by:   The FreeBSD Foundation
>
> diff --git a/lib/libc/x86/sys/__vdso_gettc.c b/lib/libc/x86/sys/__vdso_gettc.c
> index 7f224f8758cb..7a64f2a0b556 100644
> --- a/lib/libc/x86/sys/__vdso_gettc.c
> +++ b/lib/libc/x86/sys/__vdso_gettc.c
> _at__at_ -125,7 +125,7 _at__at_ struct tsc_selector_tag {
>   };
>   
>   static const struct tsc_selector_tag tsc_selector[] = {
> -	[0] = {				/* Intel or AMD Zen+, LFENCE */
> +	[0] = {				/* Intel, LFENCE */
>   		.ts_rdtsc32 =	rdtsc32_mb_lfence,
>   		.ts_rdtsc_low =	rdtsc_low_mb_lfence,
>   	},
> _at__at_ -164,9 +164,6 _at__at_ tsc_selector_idx(u_int cpu_feature)
>   	do_cpuid(1, p);
>   	cpu_id = p[0];
>   
> -	if (amd_cpu && CPUID_TO_FAMILY(cpu_id) >= 0x17)
> -		return (0);
> -
>   	if (cpu_feature != 0) {
>   		do_cpuid(0x80000000, p);
>   		cpu_exthigh = p[0];
> diff --git a/sys/x86/x86/tsc.c b/sys/x86/x86/tsc.c
> index 85924df98312..de0a1505c2f6 100644
> --- a/sys/x86/x86/tsc.c
> +++ b/sys/x86/x86/tsc.c
> _at__at_ -633,19 +633,12 _at__at_ init_TSC_tc(void)
>   
>   	/*
>   	 * Timecounter implementation selection, top to bottom:
> -	 * - For AMD Zens and newer, use LFENCE;RDTSC.
>   	 * - If RDTSCP is available, use RDTSCP.
>   	 * - If fence instructions are provided (SSE2), use LFENCE;RDTSC
>   	 *   on Intel, and MFENCE;RDTSC on AMD.
>   	 * - For really old CPUs, just use RDTSC.
>   	 */
> -	if ((cpu_vendor_id == CPU_VENDOR_AMD ||
> -	    cpu_vendor_id == CPU_VENDOR_HYGON) &&
> -	    CPUID_TO_FAMILY(cpu_id) >= 0x17) {
> -		tsc_timecounter.tc_get_timecount = shift > 0 ?
> -		    tsc_get_timecount_low_lfence :
> -		    tsc_get_timecount_lfence;
> -	} else if ((amd_feature & AMDID_RDTSCP) != 0) {
> +	if ((amd_feature & AMDID_RDTSCP) != 0) {
>   		tsc_timecounter.tc_get_timecount = shift > 0 ?
>   		    tscp_get_timecount_low : tscp_get_timecount;
>   	} else if ((cpu_feature & CPUID_SSE2) != 0 && mp_ncpus > 1) {


I have a Logitech C270 USB webcam that I use for all the online meetings 
now that everyone is working from home. (MS Teams, Google Meet, Slack, 
Zoom, whatever...).

It is supported by multimedia/webcamd and has been working mostly fine. 
(just some rare, occasional hickups)

When I started to notice the bufdaemon problems, I also noticed the 
webcam not behaving as before.

It sometimes took me two or three tries to start the camera when joining 
a meeting and once it started my video would freeze sometimes, being 
frozen for a minute or so. Sometimes when I noticed that it frooze I 
would try to restart it, and again it might take a couple of tries to 
get it working again.

With the patch it seems to work better again.


Jakob