1
Fork 0
mirror of https://github.com/RGBCube/serenity synced 2025-07-25 06:37:43 +00:00

Kernel+LibC: Allow clock_gettime() to run without syscalls

This patch adds a vDSO-like mechanism for exposing the current time as
an array of per-clock-source timestamps.

LibC's clock_gettime() calls sys$map_time_page() to map the kernel's
"time page" into the process address space (at a random address, ofc.)
This is only done on first call, and from then on the timestamps are
fetched from the time page.

This first patch only adds support for CLOCK_REALTIME, but eventually
we should be able to support all clock sources this way and get rid of
sys$clock_gettime() in the kernel entirely. :^)

Accesses are synchronized using two atomic integers that are incremented
at the start and finish of the kernel's time page update cycle.
This commit is contained in:
Andreas Kling 2021-08-10 13:44:01 +02:00
parent f02d73db4d
commit fdfc66db61
7 changed files with 117 additions and 0 deletions

View file

@ -118,6 +118,7 @@ enum class NeedsBigProcessLock {
S(listen, NeedsBigProcessLock::Yes) \
S(lseek, NeedsBigProcessLock::Yes) \
S(madvise, NeedsBigProcessLock::Yes) \
S(map_time_page, NeedsBigProcessLock::Yes) \
S(mkdir, NeedsBigProcessLock::Yes) \
S(mknod, NeedsBigProcessLock::Yes) \
S(mmap, NeedsBigProcessLock::Yes) \

30
Kernel/API/TimePage.h Normal file
View file

@ -0,0 +1,30 @@
/*
* Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Types.h>
#ifdef KERNEL
# include <Kernel/UnixTypes.h>
#else
# include <time.h>
#endif
namespace Kernel {
inline bool time_page_supports(clockid_t clock_id)
{
return clock_id == CLOCK_REALTIME;
}
struct TimePage {
volatile u32 update1;
struct timespec clocks[CLOCK_ID_COUNT];
volatile u32 update2;
};
}