Wolfgang Mauerer <wolfgang.maue...@siemens.com> writes:
> Hello,
>
> On 17/01/13 21:21, Stefan Weil wrote:
>> Am 17.01.2013 18:10, schrieb Wolfgang Mauerer:
>>> For slow targets and fast hosts, the emulation may be faster
>>> than the actual hardware, which can be undesirable for various
>>> reasons. Add a run-time option to slow down the emulation
>>> by sleeping in the CPU emulation.
>>>
> (...)
>> Please test your patch using scripts/checkpatch.pl before sending it.
>
> all stylistic issues have already been addressed in the last iteration;
> do you have additional comments on the code besides those raised in
> http://lists.gnu.org/archive/html/qemu-devel/2013-01/msg03248.html?
> Here's a pull request:
>
> The following changes since commit b5803aa3583e82e5133f7621121bc15ee694f4a1:
>
> Merge remote-tracking branch 'qemu-kvm/uq/master' into staging (2013-05-06
> 15:45:08 -0500)
>
> are available in the git repository at:
>
>
> git://github.com/siemens/qemu.git for-upstream
>
> for you to fetch changes up to 3e3a2c7158139020aa9c172ba902694e6a531cbe:
>
> Add option to slow qemu down (2013-05-07 10:43:31 +0200)
>
> ----------------------------------------------------------------
> Wolfgang Mauerer (1):
> Add option to slow qemu down
>
> cpus.c | 30 ++++++++++++++++++++++++++++++
> include/qemu-common.h | 2 ++
> qemu-options.hx | 14 ++++++++++++++
> vl.c | 10 ++++++++++
> 4 files changed, 56 insertions(+)
>
> I've also attached the patch below.
>
> Thanks, Wolfgang
>
> ######################################################################
>>From 3e3a2c7158139020aa9c172ba902694e6a531cbe Mon Sep 17 00:00:00 2001
> From: Wolfgang Mauerer <wolfgang.maue...@siemens.com>
> Date: Thu, 17 Jan 2013 15:53:39 +0100
> Subject: [PATCH] Add option to slow qemu down
>
> For slow targets and fast hosts, the emulation may be faster
> than the actual hardware, which can be undesirable for various
> reasons. Add a run-time option to slow down the emulation
> by sleeping in the CPU emulation.
>
> Signed-off-by: Wolfgang Mauerer <wolfgang.maue...@siemens.com>
> ---
> cpus.c | 30 ++++++++++++++++++++++++++++++
> include/qemu-common.h | 2 ++
> qemu-options.hx | 14 ++++++++++++++
> vl.c | 10 ++++++++++
> 4 files changed, 56 insertions(+)
>
> diff --git a/cpus.c b/cpus.c
> index c232265..2cff5f3 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -61,6 +61,7 @@
> #endif /* CONFIG_LINUX */
>
> static CPUArchState *next_cpu;
> +static bool use_slowdown;
>
> static bool cpu_thread_is_idle(CPUArchState *env)
> {
> @@ -106,6 +107,8 @@ static QEMUTimer *icount_warp_timer;
> static int64_t vm_clock_warp_start;
> static int64_t qemu_icount;
>
> +static double slowdown_factor;
> +
> typedef struct TimersState {
> int64_t cpu_ticks_prev;
> int64_t cpu_ticks_offset;
> @@ -385,6 +388,21 @@ void configure_icount(const char *option)
> qemu_get_clock_ns(vm_clock) + get_ticks_per_sec() / 10);
> }
>
> +void configure_slowdown(const char *option)
> +{
> + if (!option) {
> + return;
> + }
> +
> + slowdown_factor = strtod(option, NULL) / 100.0;
> + /* We cannot provide speedups, obviously */
> + if (slowdown_factor < 0) {
> + slowdown_factor *= -1.0;
> + }
> +
> + use_slowdown = true;
> +}
> +
> /***********************************************************/
> void hw_error(const char *fmt, ...)
> {
> @@ -1121,6 +1139,8 @@ void vm_stop_force_state(RunState state)
> static int tcg_cpu_exec(CPUArchState *env)
> {
> int ret;
> + int64_t ss = 0; /* Initialise to avoid bogous maybe-uninitialized error
> */
> + uint64_t slowdown_sleep;
> #ifdef CONFIG_PROFILER
> int64_t ti;
> #endif
> @@ -1141,7 +1161,17 @@ static int tcg_cpu_exec(CPUArchState *env)
> env->icount_decr.u16.low = decr;
> env->icount_extra = count;
> }
> + if (use_slowdown) {
> + ss = qemu_get_clock_ns(rt_clock);
> + }
> +
> ret = cpu_exec(env);
> +
> + if (use_slowdown) {
> + slowdown_sleep = qemu_get_clock_ns(rt_clock) - ss;
> + slowdown_sleep *= slowdown_factor;
> + g_usleep(slowdown_sleep / 1024);
> + }
> #ifdef CONFIG_PROFILER
> qemu_time += profile_getclock() - ti;
> #endif
> diff --git a/include/qemu-common.h b/include/qemu-common.h
> index b399d85..219993f 100644
> --- a/include/qemu-common.h
> +++ b/include/qemu-common.h
> @@ -108,6 +108,8 @@ static inline char *realpath(const char *path, char
> *resolved_path)
> void configure_icount(const char *option);
> extern int use_icount;
>
> +void configure_slowdown(const char *option);
> +
> #include "qemu/osdep.h"
> #include "qemu/bswap.h"
>
> diff --git a/qemu-options.hx b/qemu-options.hx
> index fb62b75..c764e42 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -2801,6 +2801,20 @@ order cores with complex cache hierarchies. The
> number of instructions
> executed often has little or no correlation with actual performance.
> ETEXI
>
> +DEF("slowdown", HAS_ARG, QEMU_OPTION_slowdown, \
> + "-slowdown s\n" \
> + " Slow down the CPU emulation by (approximately) s
> percent\n",
> + QEMU_ARCH_ALL)
> +STEXI
> +@item -slowdown @var{s}
> +@findex -slowdown
> +Slow down the virtual CPU by approximately s percent (i.e., for c time
> +units of execution time, sleep for c*s/100 time units). This makes it
> +possible to align the emulated machine's performance roughly with
> +the performance of physical entities, but does not provide identical
> +performance profiles since the emulation is not cycle accurate.
> +ETEXI
> +
> DEF("watchdog", HAS_ARG, QEMU_OPTION_watchdog, \
> "-watchdog i6300esb|ib700\n" \
> " enable virtual hardware watchdog [default=none]\n",
> diff --git a/vl.c b/vl.c
> index 6e6225f..27acf8b 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -2839,6 +2839,7 @@ int main(int argc, char **argv, char **envp)
> int i;
> int snapshot, linux_boot;
> const char *icount_option = NULL;
> + const char *slowdown_option = NULL;
> const char *initrd_filename;
> const char *kernel_filename, *kernel_cmdline;
> char boot_devices[33] = "";
> @@ -3751,6 +3752,9 @@ int main(int argc, char **argv, char **envp)
> case QEMU_OPTION_icount:
> icount_option = optarg;
> break;
> + case QEMU_OPTION_slowdown:
> + slowdown_option = optarg;
> + break;
> case QEMU_OPTION_incoming:
> incoming = optarg;
> runstate_set(RUN_STATE_INMIGRATE);
> @@ -4169,6 +4173,12 @@ int main(int argc, char **argv, char **envp)
> /* clean up network at qemu process termination */
> atexit(&net_cleanup);
>
> + if (slowdown_option && (kvm_enabled() || xen_enabled())) {
> + fprintf(stderr, "-slowdown is not allowed with kvm or xen\n");
> + exit(1);
Suggest to mention this in the commit message, and perhaps the manual
(STEXI..ETEXI section in qemu-options.hx).
> + }
> + configure_slowdown(slowdown_option);
> +
> if (net_init_clients() < 0) {
> exit(1);
> }
