[llvm-dev] gnu X sysv hash performance

[Rafael Avila de Espindola via llvm-dev]

Brian Cain <brian.cain at gmail.com> writes:

> On Fri, Dec 1, 2017 at 3:55 PM, Rui Ueyama via llvm-dev <
> perf usually measures cycles ("CPU_CLK_UNHALTED" for core/xeon, e.g.).   So
> it's not time but cycles.  This is a critical distinction when the thing
> being measured has delays/synchronization/disk/network I/O.

I forgot to mention this time, but I always use a tmpfs. In this case
the system tools (python for example) would be on ssd, but I discarded
a run before measuring, so I don't expect any interference from that.

> Also it looks like this report might be decomposed by some other attribute
> (DSO-at-a-time?) that would affect what "100%" means.

I sorted by dso,sym.

> Doing perf on "ninja check-llvm" seems like it would measure cycles
> contributed by lots of non-lld things, in fact it's worth ruling out
> whether it's dominated by non-lld things.  Doesn't testing itself perhaps
> spend more cycles than the linking being done here?

No, the idea was to measure the quality of the lld produced hash tables
that are used by the dynamic linker.

Cheers,
Rafael