From be6b3710c838f836544857092b407c3e374eb23c Mon Sep 17 00:00:00 2001 From: Tim Schumacher Date: Thu, 28 Jul 2022 08:31:21 +0200 Subject: [PATCH] Ports/qemu: Use the coarse monotonic clock for timing CPU ticks While this loses quite a bit of accuracy (although to no apparent decrease in emulation quality) , it helps avoiding the additional overhead of the `clock_gettime` syscall (as `CLOCK_MONOTONIC_COARSE` is forwarded using the mapped time page) and we don't have to do a HPET timer read for each tick. This results in a decrease of Serenity boot time from 1h16m down to 42m when running on Serenity. --- ...-build-system-support-for-SerenityOS.patch | 2 +- ...d-short-scan-sets-into-the-full-list.patch | 2 +- ...monotonic-clock-for-timing-CPU-ticks.patch | 27 +++++++++++++++++++ Ports/qemu/patches/ReadMe.md | 10 +++++++ 4 files changed, 39 insertions(+), 2 deletions(-) create mode 100644 Ports/qemu/patches/0003-Use-the-coarse-monotonic-clock-for-timing-CPU-ticks.patch diff --git a/Ports/qemu/patches/0001-Add-build-system-support-for-SerenityOS.patch b/Ports/qemu/patches/0001-Add-build-system-support-for-SerenityOS.patch index cc2640948f..d8e9bfc18f 100644 --- a/Ports/qemu/patches/0001-Add-build-system-support-for-SerenityOS.patch +++ b/Ports/qemu/patches/0001-Add-build-system-support-for-SerenityOS.patch @@ -8,7 +8,7 @@ Subject: [PATCH] Add build system support for SerenityOS 1 file changed, 6 insertions(+) diff --git a/configure b/configure -index 7c08c18..3177605 100755 +index 7c08c18358becf49779c876b0f3d17329df053c6..3177605054876b387cd2b93463025ee3203991e7 100755 --- a/configure +++ b/configure @@ -496,6 +496,8 @@ elif check_define __NetBSD__; then diff --git a/Ports/qemu/patches/0002-Extend-short-scan-sets-into-the-full-list.patch b/Ports/qemu/patches/0002-Extend-short-scan-sets-into-the-full-list.patch index 356a604a2b..068a94473f 100644 --- a/Ports/qemu/patches/0002-Extend-short-scan-sets-into-the-full-list.patch +++ b/Ports/qemu/patches/0002-Extend-short-scan-sets-into-the-full-list.patch @@ -10,7 +10,7 @@ sets, so extend them into a full list manually. 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/chardev/char.c b/chardev/char.c -index 0169d8d..03ce487 100644 +index 0169d8dde4b533c9cf851831b03c8adcac24cff5..03ce487a23c92b70981643bd213930f5d074afdb 100644 --- a/chardev/char.c +++ b/chardev/char.c @@ -382,11 +382,11 @@ QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename, diff --git a/Ports/qemu/patches/0003-Use-the-coarse-monotonic-clock-for-timing-CPU-ticks.patch b/Ports/qemu/patches/0003-Use-the-coarse-monotonic-clock-for-timing-CPU-ticks.patch new file mode 100644 index 0000000000..d39d7cb280 --- /dev/null +++ b/Ports/qemu/patches/0003-Use-the-coarse-monotonic-clock-for-timing-CPU-ticks.patch @@ -0,0 +1,27 @@ +From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 +From: Tim Schumacher +Date: Sat, 1 Oct 2022 02:46:48 +0200 +Subject: [PATCH] Use the coarse monotonic clock for timing CPU ticks + +While this loses quite a bit of accuracy (although to no apparent +decrease in emulation quality), it helps avoiding the additional +overhead of the `clock_gettime` syscall (as `CLOCK_MONOTONIC_COARSE` +is forwarded using the mapped time page) and we don't have to do a +HPET timer read for each tick. +--- + include/qemu/timer.h | 2 +- + 1 file changed, 1 insertion(+), 1 deletion(-) + +diff --git a/include/qemu/timer.h b/include/qemu/timer.h +index ee071e07d131641131ed9705e7407f153bbf6c67..97fb9b9ac28bd36cd7200e92c3c0c1e30858aa0d 100644 +--- a/include/qemu/timer.h ++++ b/include/qemu/timer.h +@@ -833,7 +833,7 @@ static inline int64_t get_clock(void) + { + if (use_rt_clock) { + struct timespec ts; +- clock_gettime(CLOCK_MONOTONIC, &ts); ++ clock_gettime(CLOCK_MONOTONIC_COARSE, &ts); + return ts.tv_sec * 1000000000LL + ts.tv_nsec; + } else { + /* XXX: using gettimeofday leads to problems if the date diff --git a/Ports/qemu/patches/ReadMe.md b/Ports/qemu/patches/ReadMe.md index 9ff0f4b617..5d42519184 100644 --- a/Ports/qemu/patches/ReadMe.md +++ b/Ports/qemu/patches/ReadMe.md @@ -12,3 +12,13 @@ Extend short scan sets into the full list We don't support the (apparently nonstandard) short variant of scan sets, so extend them into a full list manually. +## `0003-Use-the-coarse-monotonic-clock-for-timing-CPU-ticks.patch` + +Use the coarse monotonic clock for timing CPU ticks + +While this loses quite a bit of accuracy (although to no apparent +decrease in emulation quality), it helps avoiding the additional +overhead of the `clock_gettime` syscall (as `CLOCK_MONOTONIC_COARSE` +is forwarded using the mapped time page) and we don't have to do a +HPET timer read for each tick. +