Re: [patch] tls-2.5.31-C3

Ingo Molnar
2002-08-12T13:10:14Z

On 12 Aug 2002, Luca Barbieri wrote:

> Numbers:
> unconditional copy of 2 tls descs: 5 cycles
> this patch with 1 tls desc: 26 cycles
> this patch with 8 tls descs: 52 cycles

[ 0 tls descs: 2 cycles. ]

but yes, this is rougly what i'd say this approach costs.

> lldt: 51 cycles
> lgdt: 50 cycles
> context switch: 2000 cycles (measured with pipe read/write and vmstat so
> it's not very accurate)

> So this patch causes a 1% context switch performance drop for
> multithreaded applications.

how did you calculate this? glibc multithreaded applications can avoid the
lldt via using the TLS, and thus it's a net win.

Ingo