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From: Jan Kiszka <jan.kiszka@siemens.com>
To: Avi Kivity <avi@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Subject: Re: [PATCH 04/22] Leave inner main_loop faster on pending requests
Date: Mon, 31 Jan 2011 15:32:56 +0100	[thread overview]
Message-ID: <4D46C818.2000505@siemens.com> (raw)
In-Reply-To: <4D46B684.1050507@redhat.com>

On 2011-01-31 14:17, Avi Kivity wrote:
> On 01/31/2011 01:22 PM, Jan Kiszka wrote:
>> On 2011-01-31 10:52, Avi Kivity wrote:
>>>  On 01/27/2011 03:09 PM, Jan Kiszka wrote:
>>>>  If there is any pending request that requires us to leave the inner loop
>>>>  if main_loop, makes sure we do this as soon as possible by enforcing
>>>>  non-blocking IO processing.
>>>>
>>>>  At this change, move variable definitions out of the inner loop to
>>>>  improve readability.
>>>>
>>>>  Signed-off-by: Jan Kiszka<jan.kiszka@siemens.com>
>>>>  ---
>>>>    vl.c |   11 +++++++----
>>>>    1 files changed, 7 insertions(+), 4 deletions(-)
>>>>
>>>>  diff --git a/vl.c b/vl.c
>>>>  index 5fad700..2ebc55b 100644
>>>>  --- a/vl.c
>>>>  +++ b/vl.c
>>>>  @@ -1384,18 +1384,21 @@ qemu_irq qemu_system_powerdown;
>>>>
>>>>    static void main_loop(void)
>>>>    {
>>>>  +    bool nonblocking = false;
>>>>  +#ifdef CONFIG_PROFILER
>>>>  +    int64_t ti;
>>>>  +#endif
>>>>        int r;
>>>>
>>>>        qemu_main_loop_start();
>>>>
>>>>        for (;;) {
>>>>            do {
>>>>  -            bool nonblocking = false;
>>>>  -#ifdef CONFIG_PROFILER
>>>>  -            int64_t ti;
>>>>  -#endif
>>>>    #ifndef CONFIG_IOTHREAD
>>>>                nonblocking = cpu_exec_all();
>>>>  +            if (!vm_can_run()) {
>>>>  +                nonblocking = true;
>>>>  +            }
>>>
>>>  Doesn't this cause vmstop to spin?  We'll never execute
>>>  main_loop_wait(false) if I read the code correctly?
>>>
>>
>> The code path is not changed, we just poll instead of wait in
>> main_loop_wait.
> 
> Where do we wait then?
> 
>> Also, I didn't get your error scenario yet. Even if we left the loop
>> here, what magic would main_loop_wait do to vmstop processing? The stop
>> request is handled outside the loop, that's why we should leave ASAP.
> 
> I'm just missing the alternate place where we sleep.  If there's no such 
> place, we spin.
> 

Probably you are misled by the name of vm_can_run. It should better be
renamed to requests_pending or something like that - iow, it is only
true if some request is pending and not if just the vm is in stop mode.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

WARNING: multiple messages have this Message-ID (diff)
From: Jan Kiszka <jan.kiszka@siemens.com>
To: Avi Kivity <avi@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: [Qemu-devel] Re: [PATCH 04/22] Leave inner main_loop faster on pending requests
Date: Mon, 31 Jan 2011 15:32:56 +0100	[thread overview]
Message-ID: <4D46C818.2000505@siemens.com> (raw)
In-Reply-To: <4D46B684.1050507@redhat.com>

On 2011-01-31 14:17, Avi Kivity wrote:
> On 01/31/2011 01:22 PM, Jan Kiszka wrote:
>> On 2011-01-31 10:52, Avi Kivity wrote:
>>>  On 01/27/2011 03:09 PM, Jan Kiszka wrote:
>>>>  If there is any pending request that requires us to leave the inner loop
>>>>  if main_loop, makes sure we do this as soon as possible by enforcing
>>>>  non-blocking IO processing.
>>>>
>>>>  At this change, move variable definitions out of the inner loop to
>>>>  improve readability.
>>>>
>>>>  Signed-off-by: Jan Kiszka<jan.kiszka@siemens.com>
>>>>  ---
>>>>    vl.c |   11 +++++++----
>>>>    1 files changed, 7 insertions(+), 4 deletions(-)
>>>>
>>>>  diff --git a/vl.c b/vl.c
>>>>  index 5fad700..2ebc55b 100644
>>>>  --- a/vl.c
>>>>  +++ b/vl.c
>>>>  @@ -1384,18 +1384,21 @@ qemu_irq qemu_system_powerdown;
>>>>
>>>>    static void main_loop(void)
>>>>    {
>>>>  +    bool nonblocking = false;
>>>>  +#ifdef CONFIG_PROFILER
>>>>  +    int64_t ti;
>>>>  +#endif
>>>>        int r;
>>>>
>>>>        qemu_main_loop_start();
>>>>
>>>>        for (;;) {
>>>>            do {
>>>>  -            bool nonblocking = false;
>>>>  -#ifdef CONFIG_PROFILER
>>>>  -            int64_t ti;
>>>>  -#endif
>>>>    #ifndef CONFIG_IOTHREAD
>>>>                nonblocking = cpu_exec_all();
>>>>  +            if (!vm_can_run()) {
>>>>  +                nonblocking = true;
>>>>  +            }
>>>
>>>  Doesn't this cause vmstop to spin?  We'll never execute
>>>  main_loop_wait(false) if I read the code correctly?
>>>
>>
>> The code path is not changed, we just poll instead of wait in
>> main_loop_wait.
> 
> Where do we wait then?
> 
>> Also, I didn't get your error scenario yet. Even if we left the loop
>> here, what magic would main_loop_wait do to vmstop processing? The stop
>> request is handled outside the loop, that's why we should leave ASAP.
> 
> I'm just missing the alternate place where we sleep.  If there's no such 
> place, we spin.
> 

Probably you are misled by the name of vm_can_run. It should better be
renamed to requests_pending or something like that - iow, it is only
true if some request is pending and not if just the vm is in stop mode.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

  reply	other threads:[~2011-01-31 14:33 UTC|newest]

Thread overview: 146+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-27 13:09 [PATCH 00/22] [uq/master] Patch queue, part II Jan Kiszka
2011-01-27 13:09 ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:09 ` [PATCH 01/22] Prevent abortion on multiple VCPU kicks Jan Kiszka
2011-01-27 13:09   ` [Qemu-devel] " Jan Kiszka
2011-01-31  9:44   ` Avi Kivity
2011-01-31  9:44     ` [Qemu-devel] " Avi Kivity
2011-01-31 11:19     ` Jan Kiszka
2011-01-31 11:19       ` [Qemu-devel] " Jan Kiszka
2011-01-31 13:16       ` Avi Kivity
2011-01-31 13:16         ` [Qemu-devel] " Avi Kivity
2011-01-27 13:09 ` [PATCH 02/22] Stop current VCPU on synchronous reset requests Jan Kiszka
2011-01-27 13:09   ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:09 ` [PATCH 03/22] Process vmstop requests in IO thread Jan Kiszka
2011-01-27 13:09   ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:09 ` [PATCH 04/22] Leave inner main_loop faster on pending requests Jan Kiszka
2011-01-27 13:09   ` [Qemu-devel] " Jan Kiszka
2011-01-31  9:52   ` Avi Kivity
2011-01-31  9:52     ` [Qemu-devel] " Avi Kivity
2011-01-31 11:22     ` Jan Kiszka
2011-01-31 11:22       ` [Qemu-devel] " Jan Kiszka
2011-01-31 13:17       ` Avi Kivity
2011-01-31 13:17         ` [Qemu-devel] " Avi Kivity
2011-01-31 14:32         ` Jan Kiszka [this message]
2011-01-31 14:32           ` Jan Kiszka
2011-01-27 13:09 ` [PATCH 05/22] kvm: Report proper error on GET_VCPU_MMAP_SIZE failures Jan Kiszka
2011-01-27 13:09   ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:09 ` [PATCH 06/22] kvm: Drop redundant kvm_enabled from kvm_cpu_thread_fn Jan Kiszka
2011-01-27 13:09   ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:09 ` [PATCH 07/22] kvm: Handle kvm_init_vcpu errors Jan Kiszka
2011-01-27 13:09   ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:09 ` [PATCH 08/22] kvm: Provide sigbus services arch-independently Jan Kiszka
2011-01-27 13:09   ` [Qemu-devel] " Jan Kiszka
2011-01-27 16:39   ` Paolo Bonzini
2011-01-27 16:39     ` [Qemu-devel] " Paolo Bonzini
2011-01-30 14:51   ` Alexander Graf
2011-01-30 14:51     ` [Qemu-devel] " Alexander Graf
2011-01-27 13:09 ` [PATCH 09/22] Refactor signal setup functions in cpus.c Jan Kiszka
2011-01-27 13:09   ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:09 ` [PATCH 10/22] kvm: Set up signal mask also for !CONFIG_IOTHREAD Jan Kiszka
2011-01-27 13:09   ` [Qemu-devel] " Jan Kiszka
2011-01-28  8:08   ` Paolo Bonzini
2011-01-28  8:08     ` [Qemu-devel] " Paolo Bonzini
2011-01-27 13:09 ` [PATCH 11/22] kvm: Refactor qemu_kvm_eat_signals Jan Kiszka
2011-01-27 13:09   ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:09 ` [PATCH 12/22] kvm: Call qemu_kvm_eat_signals also under !CONFIG_IOTHREAD Jan Kiszka
2011-01-27 13:09   ` [Qemu-devel] " Jan Kiszka
2011-01-28  8:09   ` Paolo Bonzini
2011-01-28  8:09     ` [Qemu-devel] " Paolo Bonzini
2011-02-01 12:38   ` Marcelo Tosatti
2011-02-01 12:38     ` [Qemu-devel] " Marcelo Tosatti
2011-02-01 12:49     ` Marcelo Tosatti
2011-02-01 12:49       ` [Qemu-devel] " Marcelo Tosatti
2011-02-01 13:21     ` Jan Kiszka
2011-02-01 13:21       ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:09 ` [PATCH 13/22] Set up signalfd " Jan Kiszka
2011-01-27 13:09   ` [Qemu-devel] " Jan Kiszka
2011-01-28  8:11   ` Paolo Bonzini
2011-01-28  8:11     ` [Qemu-devel] " Paolo Bonzini
2011-01-27 13:09 ` [PATCH 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD Jan Kiszka
2011-01-27 13:09   ` [Qemu-devel] " Jan Kiszka
2011-01-27 14:20   ` [PATCH v2 " Jan Kiszka
2011-01-27 14:20     ` [Qemu-devel] " Jan Kiszka
2011-01-27 14:33     ` [PATCH v3 " Jan Kiszka
2011-01-27 14:33       ` [Qemu-devel] " Jan Kiszka
2011-01-31 10:03       ` Avi Kivity
2011-01-31 10:03         ` [Qemu-devel] " Avi Kivity
2011-01-31 11:27         ` Jan Kiszka
2011-01-31 11:27           ` [Qemu-devel] " Jan Kiszka
2011-01-31 12:13           ` Stefan Hajnoczi
2011-01-31 12:13             ` Stefan Hajnoczi
2011-01-31 12:18             ` Jan Kiszka
2011-01-31 12:18               ` Jan Kiszka
2011-01-31 13:35               ` Stefan Hajnoczi
2011-01-31 13:35                 ` Stefan Hajnoczi
2011-01-31 13:22           ` Avi Kivity
2011-01-31 13:22             ` [Qemu-devel] " Avi Kivity
2011-01-31 14:31             ` Jan Kiszka
2011-01-31 14:31               ` [Qemu-devel] " Jan Kiszka
2011-01-31 16:30               ` Avi Kivity
2011-01-31 16:30                 ` [Qemu-devel] " Avi Kivity
2011-02-01 12:47   ` [PATCH " Marcelo Tosatti
2011-02-01 12:47     ` [Qemu-devel] " Marcelo Tosatti
2011-02-01 13:32     ` Jan Kiszka
2011-02-01 13:32       ` [Qemu-devel] " Jan Kiszka
2011-02-01 13:48       ` Marcelo Tosatti
2011-02-01 13:48         ` [Qemu-devel] " Marcelo Tosatti
2011-02-01 13:58         ` Jan Kiszka
2011-02-01 13:58           ` [Qemu-devel] " Jan Kiszka
2011-02-01 14:10           ` Marcelo Tosatti
2011-02-01 14:10             ` [Qemu-devel] " Marcelo Tosatti
2011-02-01 14:21             ` Jan Kiszka
2011-02-01 14:21               ` [Qemu-devel] " Jan Kiszka
2011-02-01 14:37               ` Jan Kiszka
2011-02-01 14:37                 ` [Qemu-devel] " Jan Kiszka
2011-02-01 14:45                 ` Jan Kiszka
2011-02-01 14:45                   ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:09 ` [PATCH 15/22] kvm: Add MCE signal support for !CONFIG_IOTHREAD Jan Kiszka
2011-01-27 13:09   ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:10 ` [PATCH 16/22] Introduce VCPU self-signaling service Jan Kiszka
2011-01-27 13:10   ` [Qemu-devel] " Jan Kiszka
2011-02-01 13:14   ` Marcelo Tosatti
2011-02-01 13:14     ` [Qemu-devel] " Marcelo Tosatti
2011-02-01 13:33     ` Jan Kiszka
2011-02-01 13:33       ` [Qemu-devel] " Jan Kiszka
2011-02-01 13:50       ` Marcelo Tosatti
2011-02-01 13:50         ` [Qemu-devel] " Marcelo Tosatti
2011-02-01 13:59         ` Jan Kiszka
2011-02-01 13:59           ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:10 ` [PATCH 17/22] kvm: Move irqchip event processing out of inner loop Jan Kiszka
2011-01-27 13:10   ` [Qemu-devel] " Jan Kiszka
2011-01-31 10:08   ` Avi Kivity
2011-01-31 10:08     ` [Qemu-devel] " Avi Kivity
2011-01-31 11:36     ` Jan Kiszka
2011-01-31 11:36       ` [Qemu-devel] " Jan Kiszka
2011-01-31 13:04       ` Jan Kiszka
2011-01-31 13:04         ` [Qemu-devel] " Jan Kiszka
2011-01-31 15:40         ` Jan Kiszka
2011-01-31 15:40           ` [Qemu-devel] " Jan Kiszka
2011-01-31 16:38           ` Gleb Natapov
2011-01-31 16:38             ` [Qemu-devel] " Gleb Natapov
2011-01-31 16:41             ` Jan Kiszka
2011-01-31 16:41               ` [Qemu-devel] " Jan Kiszka
2011-01-31 16:45               ` Jan Kiszka
2011-01-31 16:45                 ` [Qemu-devel] " Jan Kiszka
2011-01-31 16:50               ` Gleb Natapov
2011-01-31 16:50                 ` [Qemu-devel] " Gleb Natapov
2011-01-31 16:52                 ` Jan Kiszka
2011-01-31 16:52                   ` [Qemu-devel] " Jan Kiszka
2011-01-31 16:56                   ` Gleb Natapov
2011-01-31 16:56                     ` [Qemu-devel] " Gleb Natapov
2011-01-31 18:06                     ` [PATCH v2 17&18/22] kvm: Unconditionally reenter kernel after IO exits Jan Kiszka
2011-01-31 18:06                       ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:10 ` [PATCH 18/22] " Jan Kiszka
2011-01-27 13:10   ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:10 ` [PATCH 19/22] kvm: Remove static return code of kvm_handle_io Jan Kiszka
2011-01-27 13:10   ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:10 ` [PATCH 20/22] kvm: Leave kvm_cpu_exec directly after KVM_EXIT_SHUTDOWN Jan Kiszka
2011-01-27 13:10   ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:10 ` [PATCH 21/22] Refactor kvm&tcg function names in cpus.c Jan Kiszka
2011-01-27 13:10   ` [Qemu-devel] " Jan Kiszka
2011-01-27 13:10 ` [PATCH 22/22] Fix a few coding style violations " Jan Kiszka
2011-01-27 13:10   ` [Qemu-devel] " Jan Kiszka
2011-01-31 10:12 ` [PATCH 00/22] [uq/master] Patch queue, part II Avi Kivity
2011-01-31 10:12   ` [Qemu-devel] " Avi Kivity
2011-01-31 12:03   ` Jan Kiszka
2011-01-31 12:03     ` [Qemu-devel] " Jan Kiszka

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