Messages in this thread | | | Subject | [patch 0/2] sLeAZY FPU feature | From | Arjan van de Ven <> | Date | Sat, 01 Jul 2006 19:11:33 +0200 |
| |
Hi,
the two patches in this series (the x86-64 on by me, the i386 one by Chuck Ebbert) change how the lazy fpu feature works. In the current situation, we are 100% lazy, meaning that after every context switch, the application takes a trap on the first FPU use, which then restores the FPU context.
The sLeAZY FPU patch changes this behavior; if a process has used the FPU for 5 stints at a row, the behavior becomes proactive and the FPU context is restored during the regular context switch already. This means we can avoid the trap.
The underlying assumption is that if a process uses 5 times consecutive, it's likely to do it the 6th and later times as well (eg it's not a one-off behavior).
There is a limit built in; this proactive behavior resets after 255 times, so that when a process is long lived and chances behavior, it'll still get the right behavior (for performance) after some time.
Chuck measured a +/- 0.4% performance gain, and my experiments show a similar improvement.
Greetings, Arjan van de Ven
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |