[PATCH] sched/fair: optimize entity_tick()

[PATCH] sched/fair: optimize entity_tick()

[Peng Zhang]

From: "zhangpeng.00" <zhangpeng.00@bytedance.com>

entity_tick() will be called to check preemption by calculating each
sched_entity's time_slice in a task group tree from bottom to top.

If a need_resched_flag is set by a checking of a sched_entity,
there is no necessary to check preemption of the sched_entity's
parent and ancestor entity.

So we can test if the need_resched_flag has been set before calling
check_preempt_tick() to avoid unnecessary calculations.

Signed-off-by: zhangpeng.00 <zhangpeng.00@bytedance.com>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a78d2e3b9d49..ee23afe22ac7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4757,7 +4757,7 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
 		return;
 #endif
 
-	if (cfs_rq->nr_running > 1)
+	if (cfs_rq->nr_running > 1 && !test_tsk_need_resched(rq_of(cfs_rq)->curr))
 		check_preempt_tick(cfs_rq, curr);
 }
 
-- 
2.20.1

Re: [PATCH] sched/fair: optimize entity_tick()

[Peter Zijlstra]

On Mon, Jul 18, 2022 at 05:49:37PM +0800, Peng Zhang wrote:
> From: "zhangpeng.00" <zhangpeng.00@bytedance.com>
> 
> entity_tick() will be called to check preemption by calculating each
> sched_entity's time_slice in a task group tree from bottom to top.
> 
> If a need_resched_flag is set by a checking of a sched_entity,
> there is no necessary to check preemption of the sched_entity's
> parent and ancestor entity.
> 
> So we can test if the need_resched_flag has been set before calling
> check_preempt_tick() to avoid unnecessary calculations.
> 
> Signed-off-by: zhangpeng.00 <zhangpeng.00@bytedance.com>

Optimization patches should come with numbers showing they're worth it.

Also; did you consider side-effects from check_preempt_tick(), like
clearing buddy state etc.. ?

Re: [PATCH] sched/fair: optimize entity_tick()

[kernel test robot]

Hi Peng,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on tip/sched/core]
[also build test WARNING on linus/master v5.19-rc7 next-20220718]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Peng-Zhang/sched-fair-optimize-entity_tick/20220718-175245
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 401e4963bf45c800e3e9ea0d3a0289d738005fd4
config: nios2-randconfig-s042-20220718 (https://download.01.org/0day-ci/archive/20220719/202207190234.1dmTZy65-lkp@intel.com/config)
compiler: nios2-linux-gcc (GCC) 12.1.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # apt-get install sparse
        # sparse version: v0.6.4-39-gce1a6720-dirty
        # https://github.com/intel-lab-lkp/linux/commit/9dec20bda1c5d0d7a203d393fc1ffa6e296579a9
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Peng-Zhang/sched-fair-optimize-entity_tick/20220718-175245
        git checkout 9dec20bda1c5d0d7a203d393fc1ffa6e296579a9
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=nios2 SHELL=/bin/bash drivers/target/ kernel/sched/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>


sparse warnings: (new ones prefixed by >>)
   kernel/sched/fair.c:927:34: sparse: sparse: incorrect type in argument 1 (different address spaces) @@     expected struct sched_entity *se @@     got struct sched_entity [noderef] __rcu * @@
   kernel/sched/fair.c:927:34: sparse:     expected struct sched_entity *se
   kernel/sched/fair.c:927:34: sparse:     got struct sched_entity [noderef] __rcu *
>> kernel/sched/fair.c:4760:75: sparse: sparse: incorrect type in argument 1 (different address spaces) @@     expected struct task_struct *tsk @@     got struct task_struct [noderef] __rcu *curr @@
   kernel/sched/fair.c:4760:75: sparse:     expected struct task_struct *tsk
   kernel/sched/fair.c:4760:75: sparse:     got struct task_struct [noderef] __rcu *curr
   kernel/sched/fair.c:5663:38: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected struct task_struct *curr @@     got struct task_struct [noderef] __rcu *curr @@
   kernel/sched/fair.c:5663:38: sparse:     expected struct task_struct *curr
   kernel/sched/fair.c:5663:38: sparse:     got struct task_struct [noderef] __rcu *curr
   kernel/sched/fair.c:7232:38: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected struct task_struct *curr @@     got struct task_struct [noderef] __rcu *curr @@
   kernel/sched/fair.c:7232:38: sparse:     expected struct task_struct *curr
   kernel/sched/fair.c:7232:38: sparse:     got struct task_struct [noderef] __rcu *curr
   kernel/sched/fair.c:7530:38: sparse: sparse: incorrect type in initializer (different address spaces) @@     expected struct task_struct *curr @@     got struct task_struct [noderef] __rcu *curr @@
   kernel/sched/fair.c:7530:38: sparse:     expected struct task_struct *curr
   kernel/sched/fair.c:7530:38: sparse:     got struct task_struct [noderef] __rcu *curr
   kernel/sched/fair.c:5592:35: sparse: sparse: marked inline, but without a definition
   kernel/sched/fair.c: note: in included file:
   kernel/sched/sched.h:2053:25: sparse: sparse: incompatible types in comparison expression (different address spaces):
   kernel/sched/sched.h:2053:25: sparse:    struct task_struct [noderef] __rcu *
   kernel/sched/sched.h:2053:25: sparse:    struct task_struct *
   kernel/sched/sched.h:2210:9: sparse: sparse: incompatible types in comparison expression (different address spaces):
   kernel/sched/sched.h:2210:9: sparse:    struct task_struct [noderef] __rcu *
   kernel/sched/sched.h:2210:9: sparse:    struct task_struct *
   kernel/sched/sched.h:2053:25: sparse: sparse: incompatible types in comparison expression (different address spaces):
   kernel/sched/sched.h:2053:25: sparse:    struct task_struct [noderef] __rcu *
   kernel/sched/sched.h:2053:25: sparse:    struct task_struct *
   kernel/sched/sched.h:2053:25: sparse: sparse: incompatible types in comparison expression (different address spaces):
   kernel/sched/sched.h:2053:25: sparse:    struct task_struct [noderef] __rcu *
   kernel/sched/sched.h:2053:25: sparse:    struct task_struct *

vim +4760 kernel/sched/fair.c

  4759	
> 4760		if (cfs_rq->nr_running > 1 && !test_tsk_need_resched(rq_of(cfs_rq)->curr))
  4761			check_preempt_tick(cfs_rq, curr);
  4762	}
  4763	

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp