From 429b828e7b72906241698536ae6b797a63c6749c Mon Sep 17 00:00:00 2001 From: Earl Ou Date: Fri, 11 Sep 2020 09:21:52 +0800 Subject: [PATCH] base: use setjmp to speed up fiber ucontext is an order of magnitude slower compared to most of the fiber implementation, mainly due to the additional signal mask operation. This change applies the trick provided in http://www.1024cores.net/home/lock-free-algorithms/tricks/fibers, which uses _setjmp/_longjmp to switch between contexts created by ucontext. Combine with NodeList improvement, we see 81% speed improvement with the example provided by Matthias Jung: https://gist.github.com/myzinsky/557200aa04556de44a317e0a10f51840 Compared with Accellera's SystemC, gem5 SystemC was originally 10x slower, and with this change it's about 1.8x. Change-Id: I0ffb6978e83dc8be049b750dc1baebb3d251601c Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/34356 Reviewed-by: Gabe Black Maintainer: Gabe Black Tested-by: kokoro --- src/base/fiber.cc | 13 ++++++++----- src/base/fiber.hh | 10 ++++++++++ 2 files changed, 18 insertions(+), 5 deletions(-) diff --git a/src/base/fiber.cc b/src/base/fiber.cc index 3d2e2e947..fe1bad09a 100644 --- a/src/base/fiber.cc +++ b/src/base/fiber.cc @@ -145,10 +145,12 @@ Fiber::start() setStarted(); - // Swap back to the parent context which is still considered "current", - // now that we're ready to go. - int ret M5_VAR_USED = swapcontext(&ctx, &_currentFiber->ctx); - panic_if(ret == -1, strerror(errno)); + if (_setjmp(jmp) == 0) { + // Swap back to the parent context which is still considered "current", + // now that we're ready to go. + int ret = swapcontext(&ctx, &_currentFiber->ctx); + panic_if(ret == -1, strerror(errno)); + } // Call main() when we're been reactivated for the first time. main(); @@ -175,7 +177,8 @@ Fiber::run() Fiber *prev = _currentFiber; Fiber *next = this; _currentFiber = next; - swapcontext(&prev->ctx, &next->ctx); + if (_setjmp(prev->jmp) == 0) + _longjmp(next->jmp, 1); } Fiber *Fiber::currentFiber() { return _currentFiber; } diff --git a/src/base/fiber.hh b/src/base/fiber.hh index dc7ef019f..be8937f18 100644 --- a/src/base/fiber.hh +++ b/src/base/fiber.hh @@ -39,6 +39,12 @@ #include #endif +// Avoid fortify source for longjmp to work between ucontext stacks. +#pragma push_macro("__USE_FORTIFY_LEVEL") +#undef __USE_FORTIFY_LEVEL +#include +#pragma pop_macro("__USE_FORTIFY_LEVEL") + #include #include @@ -137,6 +143,10 @@ class Fiber void start(); ucontext_t ctx; + // ucontext is slow in swapcontext. Here we use _setjmp/_longjmp to avoid + // the additional signals for speed up. + jmp_buf jmp; + Fiber *link; // The stack for this context, or a nullptr if allocated elsewhere. -- 2.30.2