Re: Some interesting results from tweaking spinlocks

[2002-01-05 17:04] Tom Lane said:
| Brent Verner <brent@rcfile.org> writes:
| > Using a single-processor machine, we're not going to get any lower 
| > sleep times than ~10ms from either usleep or select on linux, and 
| > usleep is always longer.
| 
| Ah, so usleep is just being stricter about rounding up the requested
| delay?  That would explain the results all right.

The only difference I see is that sys_nanosleep gets its actual timeout
value using timespec_to_jiffies(), and do_select leaves the specified
delay untouched.

| > Looks like increasing spins allows
| > the process to get the lock before the usleep/select is run 
| 
| Right.  Up to a point, increasing spins improves the odds of acquiring
| the lock without having to release the processor.
| 
| What I should've thought of is to try sched_yield() as well, which is
| the operation we *really* want here, and it is available on this version
| of Linux.  Off to run another batch of tests ...

yes.  using just sched_yield() inside the TAS loop appears to give
better performance on both freebsd and linux (single-proc); in
particular, it _looks_ like there is a 8-10% performance gain at
32 clients.

btw, what are y'all using to generate these nifty graphs?

thanks. brent

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