[v6] powerpc/vdso64: Add support for CLOCK_{REALTIME/MONOTONIC}_COARSE

[Michael Ellerman]

On Mon, 2017-10-16 at 05:49:14 UTC, Santosh Sivaraj wrote:
> Current vDSO64 implementation does not have support for coarse clocks
> (CLOCK_MONOTONIC_COARSE, CLOCK_REALTIME_COARSE), for which it falls back
> to system call, increasing the response time, vDSO implementation reduces
> the cycle time. Below is a benchmark of the difference in execution times.
> 
> (Non-coarse clocks are also included just for completion)
> 
> clock-gettime-realtime: syscall: 172 nsec/call
> clock-gettime-realtime:    libc: 28 nsec/call
> clock-gettime-realtime:    vdso: 22 nsec/call
> clock-gettime-monotonic: syscall: 171 nsec/call
> clock-gettime-monotonic:    libc: 30 nsec/call
> clock-gettime-monotonic:    vdso: 25 nsec/call
> clock-gettime-realtime-coarse: syscall: 153 nsec/call
> clock-gettime-realtime-coarse:    libc: 16 nsec/call
> clock-gettime-realtime-coarse:    vdso: 10 nsec/call
> clock-gettime-monotonic-coarse: syscall: 167 nsec/call
> clock-gettime-monotonic-coarse:    libc: 17 nsec/call
> clock-gettime-monotonic-coarse:    vdso: 11 nsec/call
> 
> CC: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> Reviewed-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
> Signed-off-by: Santosh Sivaraj <santosh at fossix.org>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/5c929885f1bb4b77f85b1769c49405

cheers