On Thu, May 19, 2016 at 02:24:57PM +0200, Peter Zijlstra wrote: > On Thu, May 05, 2016 at 08:44:05PM -0000, Thomas Gleixner wrote: > > From: Sebastian Siewior <bige...@linutronix.de> > > > > The per process hash is allocated on the fly at the first futex operation > > of a > > process. The size of the hash is determined by a system wide default setting > > controlled by the sys admin, This is suboptimal for RT applications and > > applications with pathological futex abuse, > > > > - For RT applications its important to allocate the per process hash > > before the > > first futex operation to avoid the allocation on the first futex > > operation. > > > > - For pathological applications which use gazillions of futexes its useful > > to > > allocate a hash greater than the default hash size. > > > > Add a futex op which allows to preallocate the hash with the requested > > size. The size is limited by the systemwide maximum hash size, which can be > > set by the admin. The requested size is rounded up to the next order of 2. > > > > The function can be called several times, but ony the first call results in > > a > > hash allocation of the requested size as there is no non-intrusive way to > > reallocate/rehash in a multithreaded application. > > > > Note, that this call must be issued before the first futex operation in the > > process because that would automatically allocate the default sized hash. > > > > The function returns the actual hash size or 0 if the global hash is used. > > The > > latter is the case on UP and in the rare case that the allocation failed and > > the global hash is used as a fallback. > > OK, so no on-line rehashing possible?
It doesn't do it currently... did you see something that makes it impossible to add? -- Darren Hart Intel Open Source Technology Center
