linux/arch/um/kernel/skas/clone.c
Anton Ivanov 2eb5f31bc4 um: Switch clocksource to hrtimers
UML is using an obsolete itimer call for
all timers and "polls" for kernel space timer firing
in its userspace portion resulting in a long list
of bugs and incorrect behaviour(s). It also uses
ITIMER_VIRTUAL for its timer which results in the
timer being dependent on it running and the cpu
load.

This patch fixes this by moving to posix high resolution
timers firing off CLOCK_MONOTONIC and relaying the timer
correctly to the UML userspace.

Fixes:
 - crashes when hosts suspends/resumes
 - broken userspace timers - effecive ~40Hz instead
   of what they should be. Note - this modifies skas behavior
   by no longer setting an itimer per clone(). Timer events
   are relayed instead.
 - kernel network packet scheduling disciplines
 - tcp behaviour especially under load
 - various timer related corner cases

Finally, overall responsiveness of userspace is better.

Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Anton Ivanov <aivanov@brocade.com>
[rw: massaged commit message]
Signed-off-by: Richard Weinberger <richard@nod.at>
2015-11-06 22:54:49 +01:00

53 lines
1.2 KiB
C

/*
* Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
* Copyright (C) 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
* Licensed under the GPL
*/
#include <signal.h>
#include <sched.h>
#include <asm/unistd.h>
#include <sys/time.h>
#include <as-layout.h>
#include <ptrace_user.h>
#include <stub-data.h>
#include <sysdep/stub.h>
/*
* This is in a separate file because it needs to be compiled with any
* extraneous gcc flags (-pg, -fprofile-arcs, -ftest-coverage) disabled
*
* Use UM_KERN_PAGE_SIZE instead of PAGE_SIZE because that calls getpagesize
* on some systems.
*/
void __attribute__ ((__section__ (".__syscall_stub")))
stub_clone_handler(void)
{
struct stub_data *data = (struct stub_data *) STUB_DATA;
long err;
err = stub_syscall2(__NR_clone, CLONE_PARENT | CLONE_FILES | SIGCHLD,
STUB_DATA + UM_KERN_PAGE_SIZE / 2 - sizeof(void *));
if (err != 0)
goto out;
err = stub_syscall4(__NR_ptrace, PTRACE_TRACEME, 0, 0, 0);
if (err)
goto out;
remap_stack(data->fd, data->offset);
goto done;
out:
/*
* save current result.
* Parent: pid;
* child: retcode of mmap already saved and it jumps around this
* assignment
*/
data->err = err;
done:
trap_myself();
}