FreeBSD MySQL still WAY slower than Linux

[Jon Dama]

Just wondering:

How much processor migration takes place on linux mysql?
Do the threads mostly stick to the same processors?

I've noticed that on FreeBSD the 4BSD scheduler doesn't do much to
preserve cache coherency.

What sort of cache/TLB misses do you see running mysql linux vs. mysql
freebsd?

-Jon

On Sat, 11 Jun 2005, Robert Watson wrote:

>
> On Fri, 10 Jun 2005, Steve Roome wrote:
>
> > We're using mostly:
> >
> >  5.4-STABLE FreeBSD 5.4-STABLE #0: Mon Jun 6 12:22:18 BST 2005
>
> In my experience, the following factors make a big performance difference:
>
> - Thread package.  In 5.x, you get process scope threads by default, but
>    it turns out MySQL is tuned for system scope threads, and this is
>    particularly visible in the supersmack benchmark, which competes many
>    client processes against a few server threads.  I'm not sure what the
>    condition is of libthr on 5.x, but you could give it a spin.  In 6.x,
>    libthr has been largely rewritten and is a great deal faster.  I think
>    there's a compile-time option to make libpthread use system scope
>    threads but the details ellude me.  The Linuxthreads library may well
>    provide a substantial improvement -- not as good for MySQL as the 6.x
>    libthr, but perhaps much more appropriate than libpthread.
>
> - Locking model.  Make sure that debug.mpsafenet is set to 1 (i.e., there
>    aren't components in the kernel that force Giant over the network stack.
>    Chances are there are none, but it's worth checking).
>
> - Twiddling hyper-threading, which helps or hurts differently in various
>    configurations.
>
> - On a UP system, consider compiling a kernel without "options SMP" to
>    reduce locking overhead.
>
> I've found the single largest remaining factor to be threading package --
> over the past year or so I've about doubled MySQL performance on 5.x
> leading up to 5.3, largely through SMP locking work, but the remainder of
> the difference appears to be in the threading package.
>
> Robert N M Watson
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