Re: need better POSIX semaphore support

On Sunday 30 May 2010 11:06:22 am Kostik Belousov wrote:
> On Sun, May 30, 2010 at 06:30:35PM +0400, Dmitry Marakasov wrote:
> > Hi!
> > 
> > Not long ago, POSIX semaphores support was enabled by default as it's
> > becoming more widely used, by e.g. firefox. However, the support
> > for these is still incomplete: we only have systemwide limit of 30
> > semaphores, and that doesn't seem to be configurable neither online with
> > sysctl, nor at boottime from loader.conf. I only was able to raise
> > semaphore count by changing SEM_MAX in kernel sources.
> > 
> > The real appliaction which needs more semaphores is lightspark
> > (graphics/lightspark-devel) flash plugin - it uses ~40 sems for simple
> > clips and ~250 for something like youtube videos.
> > 
> > Until there more apps that require proper semaphore support, I guess
> > we need to improve it asap. Given the amount of memory used by ksem,
> > the least can be done is SEM_MAX bumped up to 5120 or so for
> > non-embedded kernels. 5120 semaphores require just 644k of kernel
> > memory (judging by vmstat), and is "ought to be enough for anybody".
> > Another good thing would be to make it configurable at boot-time
> > or even better in runtime.
> 
> HEAD contains different implementation. Apparently, it did not made
> into stable/8 yet, so it will not appear in the 8.1.

The one thing I don't like about this approach is you can write the variable 
even when sem.ko isn't loaded.  The SEM_* values should really only exist when 
sem.ko is loaded I think, which requires moving them into uipc_sem.c.

> Try this, I could try to squeeze it into 8.1.
> 
> diff --git a/sys/kern/posix4_mib.c b/sys/kern/posix4_mib.c
> index 5242b31..41e28da 100644
> --- a/sys/kern/posix4_mib.c
> +++ b/sys/kern/posix4_mib.c
> _at__at_ -57,6 +57,9 _at__at_ SYSCTL_DECL(_p1003_1b);
>  #define P1B_SYSCTL(num, name)  \
>  SYSCTL_INT(_p1003_1b, num, \
>  	name, CTLFLAG_RD, facility + num - 1, 0, "");
> +#define P1B_SYSCTL_RW(num, name)  \
> +SYSCTL_INT(_p1003_1b, num, \
> +	name, CTLFLAG_RW, facility + num - 1, 0, "");
>  
>  #else
>  
> _at__at_ -65,6 +68,9 _at__at_ SYSCTL_DECL(_kern_p1003_1b);
>  #define P1B_SYSCTL(num, name)  \
>  SYSCTL_INT(_kern_p1003_1b, OID_AUTO, \
>  	name, CTLFLAG_RD, facility + num - 1, 0, "");
> +#define P1B_SYSCTL_RW(num, name)  \
> +SYSCTL_INT(_kern_p1003_1b, OID_AUTO, \
> +	name, CTLFLAG_RW, facility + num - 1, 0, "");
>  SYSCTL_NODE(_kern, OID_AUTO, p1003_1b, CTLFLAG_RW, 0, "P1003.1B");
>  
>  #endif
> _at__at_ -91,7 +97,7 _at__at_ P1B_SYSCTL(CTL_P1003_1B_DELAYTIMER_MAX, delaytimer_max);
>  P1B_SYSCTL(CTL_P1003_1B_MQ_OPEN_MAX, mq_open_max);
>  P1B_SYSCTL(CTL_P1003_1B_PAGESIZE, pagesize);
>  P1B_SYSCTL(CTL_P1003_1B_RTSIG_MAX, rtsig_max);
> -P1B_SYSCTL(CTL_P1003_1B_SEM_NSEMS_MAX, sem_nsems_max);
> +P1B_SYSCTL_RW(CTL_P1003_1B_SEM_NSEMS_MAX, sem_nsems_max);
>  P1B_SYSCTL(CTL_P1003_1B_SEM_VALUE_MAX, sem_value_max);
>  P1B_SYSCTL(CTL_P1003_1B_SIGQUEUE_MAX, sigqueue_max);
>  P1B_SYSCTL(CTL_P1003_1B_TIMER_MAX, timer_max);
> 

-- 
John Baldwin