Date: Tue, 1 Jun 2010 13:19:22 -0400 From: John Baldwin <jhb@freebsd.org> To: Kostik Belousov <kostikbel@gmail.com> Cc: freebsd-current@freebsd.org, freebsd-stable@freebsd.org, Dmitry Marakasov <amdmi3@amdmi3.ru> Subject: Re: need better POSIX semaphore support Message-ID: <201006011319.22275.jhb@freebsd.org> In-Reply-To: <20100601170526.GJ83316@deviant.kiev.zoral.com.ua> References: <20100530143034.GH43302@hades.panopticon> <201006011141.09699.jhb@freebsd.org> <20100601170526.GJ83316@deviant.kiev.zoral.com.ua>
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On Tuesday 01 June 2010 1:05:26 pm Kostik Belousov wrote: > On Tue, Jun 01, 2010 at 11:41:09AM -0400, John Baldwin wrote: > > 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. > > I think the values should exist always, because sysconf(3) returns > error (i.e. -1 and errno set) when sysctl fails. sysconf(3) interprets > 0 result as "feature not supported". > > I modified the patch to only allow change of value when the module is loaded. > Also, the module unload now clears mib. As usual, module unload races are > not handled. I think this looks good, thanks! -- John Baldwin
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