From: Zhenzhong Duan <zhenzhong.duan@oracle.com>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: linux-kernel@vger.kernel.org, pbonzini@redhat.com,
rkrcmar@redhat.com, rafael.j.wysocki@intel.com,
joao.m.martins@oracle.com, mtosatti@redhat.com,
kvm@vger.kernel.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH RESEND v2 3/4] cpuidle-haltpoll: ensure cpu_halt_poll_us in right scope
Date: Sun, 17 Nov 2019 16:57:57 +0800 [thread overview]
Message-ID: <5ff7cb30-b6fb-d9df-ee8d-bf21b95c9cb1@oracle.com> (raw)
In-Reply-To: <6161954.sKiXg2khOt@kreacher>
On 2019/11/15 18:45, Rafael J. Wysocki wrote:
> On Wednesday, November 6, 2019 12:55:01 PM CET Zhenzhong Duan wrote:
>> As user can adjust guest_halt_poll_grow_start and guest_halt_poll_ns
>> which leads to cpu_halt_poll_us beyond the two boundaries. This patch
>> ensures cpu_halt_poll_us in that scope.
>>
>> If guest_halt_poll_shrink is 0, shrink the cpu_halt_poll_us to
>> guest_halt_poll_grow_start instead of 0. To disable poll we can set
>> guest_halt_poll_ns to 0.
>>
>> If user wrongly set guest_halt_poll_grow_start > guest_halt_poll_ns > 0,
>> guest_halt_poll_ns take precedency and poll time is a fixed value of
>> guest_halt_poll_ns.
>>
>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
>> ---
>> drivers/cpuidle/governors/haltpoll.c | 28 +++++++++++++---------------
>> 1 file changed, 13 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/cpuidle/governors/haltpoll.c b/drivers/cpuidle/governors/haltpoll.c
>> index 660859d..4a39df4 100644
>> --- a/drivers/cpuidle/governors/haltpoll.c
>> +++ b/drivers/cpuidle/governors/haltpoll.c
>> @@ -97,32 +97,30 @@ static int haltpoll_select(struct cpuidle_driver *drv,
>>
>> static void adjust_poll_limit(struct cpuidle_device *dev, unsigned int block_us)
>> {
>> - unsigned int val;
>> + unsigned int val = dev->poll_limit_ns;
> Not necessary to initialize it here.
Then an random val may bypass all the check and get assigned to dev->poll_limit_ns
if guest_halt_poll_grow_start< block_ns< uninitialized val< guest_halt_poll_ns
With my change, dev->poll_limit_ns will not be changed in that case, logic same as original code.
>
>> u64 block_ns = block_us*NSEC_PER_USEC;
>>
>> /* Grow cpu_halt_poll_us if
>> - * cpu_halt_poll_us < block_ns < guest_halt_poll_us
>> + * cpu_halt_poll_us < block_ns <= guest_halt_poll_us
> You could update the comment to say "dev->poll_limit_ns" instead of
> "cpu_halt_poll_us" while at it.
Will do, also guest_halt_poll_us to guest_halt_poll_ns
>
>> */
>> - if (block_ns > dev->poll_limit_ns && block_ns <= guest_halt_poll_ns) {
>> + if (block_ns > dev->poll_limit_ns && block_ns <= guest_halt_poll_ns &&
>> + guest_halt_poll_grow)
> The "{" brace is still needed as per the coding style and I'm not sure why
> to avoid guest_halt_poll_grow equal to zero here?
Will add "{}" and remove guest_halt_poll_grow check. My inital thought was to prevent
dev->poll_limit_ns get shrinked with guest_halt_poll_grow=0.
>
>> val = dev->poll_limit_ns * guest_halt_poll_grow;
>> -
>> - if (val < guest_halt_poll_grow_start)
>> - val = guest_halt_poll_grow_start;
>> - if (val > guest_halt_poll_ns)
>> - val = guest_halt_poll_ns;
>> -
>> - dev->poll_limit_ns = val;
>> - } else if (block_ns > guest_halt_poll_ns &&
>> - guest_halt_poll_allow_shrink) {
>> + else if (block_ns > guest_halt_poll_ns &&
>> + guest_halt_poll_allow_shrink) {
>> unsigned int shrink = guest_halt_poll_shrink;
>>
>> - val = dev->poll_limit_ns;
>> if (shrink == 0)
>> - val = 0;
>> + val = guest_halt_poll_grow_start;
> That's going to be corrected below, so the original code would be fine.
val was assigned twice using 'val = 0' while it's once with my change, optimal a bit?
>
>> else
>> val /= shrink;
> Here you can do
>
> val = dev->poll_limit_ns / shrink;
Any special reason?Looks no difference for me.
>
>> - dev->poll_limit_ns = val;
>> }
>> + if (val < guest_halt_poll_grow_start)
>> + val = guest_halt_poll_grow_start;
> Note that guest_halt_poll_grow_start is in us (as per the comment next to its
> definition and the initial value). That is a bug in the original code too,
> but anyway.
Good catch! will fix the comment. The default 50000ns vs 50000us, looks author means ns.
guest_halt_poll_ns defaults to 200000, also hints ns for guest_halt_poll_grow_start.
Thanks
Zhenzhong
next prev parent reply other threads:[~2019-11-17 8:58 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-06 11:54 [PATCH RESEND v2 0/4] misc fixes on halt-poll code for both KVM and guest Zhenzhong Duan
2019-11-06 11:54 ` [PATCH RESEND v2 1/4] cpuidle-haltpoll: ensure grow start value is nonzero Zhenzhong Duan
2019-11-15 10:06 ` Rafael J. Wysocki
2019-11-15 10:16 ` Rafael J. Wysocki
2019-11-15 10:26 ` Rafael J. Wysocki
2019-11-17 9:02 ` Zhenzhong Duan
2019-11-06 11:55 ` [PATCH RESEND v2 2/4] KVM: " Zhenzhong Duan
2019-11-11 20:13 ` Sean Christopherson
2019-11-12 12:19 ` Zhenzhong Duan
2019-11-06 11:55 ` [PATCH RESEND v2 3/4] cpuidle-haltpoll: ensure cpu_halt_poll_us in right scope Zhenzhong Duan
2019-11-15 10:45 ` Rafael J. Wysocki
2019-11-17 8:57 ` Zhenzhong Duan [this message]
2019-11-06 11:55 ` [PATCH RESEND v2 4/4] KVM: ensure vCPU halt_poll_us " Zhenzhong Duan
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