[PATCH] Removal of redundant check

[PATCH] Removal of redundant check

[Praveen Kumar]

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The patch gets rid of a redundant check in csched_vcpu_acct which adds
more code clarity and performance. This patch also adds an ASSERT to
the same effect, in order to make assumption ( i.e., no calling this on
idle vcpus) even more clear and as a guard for future mis-use.

Signed-off-by: Praveen Kumar <kpraveen.lkml@gmail.com>

diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index fc3a321..dfe8545 100644
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -941,6 +941,7 @@ csched_vcpu_acct(struct csched_private *prv,
unsigned int cpu)

     ASSERT( current->processor == cpu );
     ASSERT( svc->sdom != NULL );
+    ASSERT( !is_idle_vcpu(svc->vcpu) );

     /*
      * If this VCPU's priority was boosted when it last awoke, reset
it.
@@ -957,8 +958,7 @@ csched_vcpu_acct(struct csched_private *prv,
unsigned int cpu)
     /*
      * Update credits
      */
-    if ( !is_idle_vcpu(svc->vcpu) )
-        burn_credits(svc, NOW());
+    burn_credits(svc, NOW());

     /*
      * Put this VCPU and domain back on the active list if it was

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The patch gets rid of a redundant check in csched_vcpu_acct which adds more code
clarity and performance. This patch also adds an ASSERT to the same effect, in
order to make assumption ( i.e., no calling this on idle vcpus) even more clear
and as a guard for future mis-use.

Signed-off-by: Praveen Kumar <kpraveen.lkml@gmail.com>

diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index fc3a321..dfe8545 100644
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -941,6 +941,7 @@ csched_vcpu_acct(struct csched_private *prv, unsigned int cpu)

     ASSERT( current->processor == cpu );
     ASSERT( svc->sdom != NULL );
+    ASSERT( !is_idle_vcpu(svc->vcpu) );

     /*
      * If this VCPU's priority was boosted when it last awoke, reset it.
@@ -957,8 +958,7 @@ csched_vcpu_acct(struct csched_private *prv, unsigned int cpu)
     /*
      * Update credits
      */
-    if ( !is_idle_vcpu(svc->vcpu) )
-        burn_credits(svc, NOW());
+    burn_credits(svc, NOW());

     /*
      * Put this VCPU and domain back on the active list if it was

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Re: [PATCH] Removal of redundant check

[Dario Faggioli]

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Hello!

Glad to see he patch here. One thing, about the subject line: it should
contains "tags", i.e., an indication of the component that the patch
affects.

So, for example, in this case, the patch touches Credit1, which means
scheduling inside Xen. So, a valid subject line could be:

 [PATCH] xen: sched: removal of redundant check in Credit

or:

 [PATCH] xen: credit: removal of redundant check

On Wed, 2016-12-14 at 23:49 +0530, Praveen Kumar wrote:
> The patch gets rid of a redundant check in csched_vcpu_acct which
> adds
> more code clarity and performance. 
>
I'd remove "which adds more code clarity and performance" and put here
something like:

"In fact, the function is only called from csched_tick, which already
checks that current is not the idle vcpu."

> This patch also adds an ASSERT to
> the same effect, in order to make assumption ( i.e., no calling this
> on
> idle vcpus) even more clear and as a guard for future mis-use.
> 
> Signed-off-by: Praveen Kumar <kpraveen.lkml@gmail.com>
> 
Apart from what just said above, the patch looks good to me. Can you
send version 2 with the changelog updated?

Oh, and I see that you are both inlining in the email and attaching the
patch. I personally don't particularly mind, but that may make the life
of a committer (the person which, when the patch will have all the
Acks, will put it inside the Xen git repository) a bit more difficult.

So, this is mostly George's call, I think, but FWIW, I'd suggest you
avoid doing that. :-)

Thanks and Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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Re: [PATCH] Removal of redundant check

[George Dunlap]

> On Dec 15, 2016, at 8:18 AM, Dario Faggioli <dario.faggioli@citrix.com> wrote:

> Oh, and I see that you are both inlining in the email and attaching the
> patch. I personally don't particularly mind, but that may make the life
> of a committer (the person which, when the patch will have all the
> Acks, will put it inside the Xen git repository) a bit more difficult.
> 
> So, this is mostly George's call, I think, but FWIW, I'd suggest you
> avoid doing that. :-)

git send-email is usually easier for everyone (both submitter and committer); but some people’s corporate setup doesn’t allow its use.  Jan’s patches are always pasted in-line and attached, for instance.

 -George
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