Messages in this thread | | | Date | Sat, 12 Jun 2021 22:31:38 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v9] pgo: add clang's Profile Guided Optimization infrastructure |
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On Sat, Jun 12, 2021 at 01:20:15PM -0700, Fangrui Song wrote:
> For applications, I think instrumentation based PGO can be 1%~4% faster > than sample-based PGO (e.g. AutoFDO) on x86.
Why? What specifically is missed by sample-based? I thought that LBR augmented samples were very useful for exactly this.
> Sample-based PGO has CPU requirement (e.g. Performance Monitoring Unit). > (my gut feeling is that there may be larger gap between instrumentation > based PGO and sample-based PGO for aarch64/ppc64, even though they can > use sample-based PGO.) > Instrumentation based PGO can be ported to more architectures.
Every architecture that cares about performance had better have a hardware PMU. Both argh64 and ppc64 have one.
> In addition, having an infrastructure for instrumentation based PGO > makes it easy to deploy newer techniques like context-sensitive PGO > (just changed compile options; it doesn't need new source level > annotation).
What's this context sensitive stuff you speak of? The link provided earlier is devoid of useful information.
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