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Re: revivesa status 2008/07/09

On Jul 12, 2008, at 10:07 AM, Gary Thorpe wrote:

The advantages of SA are supposed to be on *I/O* bound workloads because it can reduce overhead due to kernel context switches by doing userland switches where appropriate (according to previous benchmarks, research etc.), but I could be wron on this.

No. I/O bound switching in SA requires a kernel context switch (because the thread blocks in the kernel).

SA is a win only when you have MANY threads blocking on user-space synchronization primitives, and in that case, the benefit is diminished greatly when you have threads being time-sliced against each other because the timer firing involves the kernel (our libpthread time-sliced by default).

-- thorpej

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