Re: revivesa status 2008/07/09

[Jason Thorpe <thorpej%shagadelic.org@localhost>]

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