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https://github.com/SerenityOS/serenity
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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.
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@ -8,7 +8,7 @@ Subject: [PATCH] Add build system support for SerenityOS
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1 file changed, 6 insertions(+)
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diff --git a/configure b/configure
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index 7c08c18..3177605 100755
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index 7c08c18358becf49779c876b0f3d17329df053c6..3177605054876b387cd2b93463025ee3203991e7 100755
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--- a/configure
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+++ b/configure
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@@ -496,6 +496,8 @@ elif check_define __NetBSD__; then
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@ -10,7 +10,7 @@ sets, so extend them into a full list manually.
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1 file changed, 2 insertions(+), 2 deletions(-)
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diff --git a/chardev/char.c b/chardev/char.c
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index 0169d8d..03ce487 100644
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index 0169d8dde4b533c9cf851831b03c8adcac24cff5..03ce487a23c92b70981643bd213930f5d074afdb 100644
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--- a/chardev/char.c
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+++ b/chardev/char.c
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@@ -382,11 +382,11 @@ QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename,
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@ -0,0 +1,27 @@
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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Tim Schumacher <timschumi@gmx.de>
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Date: Sat, 1 Oct 2022 02:46:48 +0200
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Subject: [PATCH] Use the coarse monotonic clock for timing CPU ticks
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While this loses quite a bit of accuracy (although to no apparent
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decrease in emulation quality), it helps avoiding the additional
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overhead of the `clock_gettime` syscall (as `CLOCK_MONOTONIC_COARSE`
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is forwarded using the mapped time page) and we don't have to do a
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HPET timer read for each tick.
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---
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include/qemu/timer.h | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/include/qemu/timer.h b/include/qemu/timer.h
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index ee071e07d131641131ed9705e7407f153bbf6c67..97fb9b9ac28bd36cd7200e92c3c0c1e30858aa0d 100644
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--- a/include/qemu/timer.h
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+++ b/include/qemu/timer.h
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@@ -833,7 +833,7 @@ static inline int64_t get_clock(void)
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{
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if (use_rt_clock) {
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struct timespec ts;
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- clock_gettime(CLOCK_MONOTONIC, &ts);
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+ clock_gettime(CLOCK_MONOTONIC_COARSE, &ts);
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return ts.tv_sec * 1000000000LL + ts.tv_nsec;
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} else {
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/* XXX: using gettimeofday leads to problems if the date
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@ -12,3 +12,13 @@ Extend short scan sets into the full list
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We don't support the (apparently nonstandard) short variant of scan
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sets, so extend them into a full list manually.
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## `0003-Use-the-coarse-monotonic-clock-for-timing-CPU-ticks.patch`
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Use the coarse monotonic clock for timing CPU ticks
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While this loses quite a bit of accuracy (although to no apparent
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decrease in emulation quality), it helps avoiding the additional
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overhead of the `clock_gettime` syscall (as `CLOCK_MONOTONIC_COARSE`
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is forwarded using the mapped time page) and we don't have to do a
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HPET timer read for each tick.
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