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SubjectRe: [RFC] vmstat: Avoid waking up idle-cpu to service shepherd work
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On 28 March 2015 at 19:14, Peter Zijlstra <peterz@infradead.org> wrote:
> Yeah, something like the below (at the very end) should ensure the thing
> is cacheline aligned, that should give us a fair few bits.

> ---
> kernel/time/timer.c | 36 ++++++++----------------------------
> 1 file changed, 8 insertions(+), 28 deletions(-)
>
> diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> index 2d3f5c504939..c8c45bf50b2e 100644
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -93,6 +93,7 @@ struct tvec_base {
> struct tvec_base boot_tvec_bases;
> EXPORT_SYMBOL(boot_tvec_bases);
> static DEFINE_PER_CPU(struct tvec_base *, tvec_bases) = &boot_tvec_bases;
> +static DEFINE_PER_CPU(struct tvec_base, __tvec_bases);
>
> /* Functions below help us manage 'deferrable' flag */
> static inline unsigned int tbase_get_deferrable(struct tvec_base *base)
> @@ -1534,46 +1535,25 @@ EXPORT_SYMBOL(schedule_timeout_uninterruptible);
>
> static int init_timers_cpu(int cpu)
> {
> - int j;
> - struct tvec_base *base;
> + struct tvec_base *base = per_cpu(tvec_bases, cpu);
> static char tvec_base_done[NR_CPUS];
> + int j;
>
> if (!tvec_base_done[cpu]) {
> static char boot_done;
>
> - if (boot_done) {
> - /*
> - * The APs use this path later in boot
> - */
> - base = kzalloc_node(sizeof(*base), GFP_KERNEL,
> - cpu_to_node(cpu));
> - if (!base)
> - return -ENOMEM;
> -
> - /* Make sure tvec_base has TIMER_FLAG_MASK bits free */
> - if (WARN_ON(base != tbase_get_base(base))) {
> - kfree(base);
> - return -ENOMEM;
> - }
> - per_cpu(tvec_bases, cpu) = base;
> + if (!boot_done) {
> + boot_done = 1; /* skip the boot cpu */
> } else {
> - /*
> - * This is for the boot CPU - we use compile-time
> - * static initialisation because per-cpu memory isn't
> - * ready yet and because the memory allocators are not
> - * initialised either.
> - */
> - boot_done = 1;
> - base = &boot_tvec_bases;
> + base = per_cpu_ptr(&__tvec_bases);
> + per_cpu(tvec_bases, cpu) = base;
> }
> +
> spin_lock_init(&base->lock);
> tvec_base_done[cpu] = 1;
> base->cpu = cpu;
> - } else {
> - base = per_cpu(tvec_bases, cpu);
> }
>
> -
> for (j = 0; j < TVN_SIZE; j++) {
> INIT_LIST_HEAD(base->tv5.vec + j);
> INIT_LIST_HEAD(base->tv4.vec + j);

Even after this with following diff gives me the same warning on blackfin..

diff --git a/include/linux/timer.h b/include/linux/timer.h
index 8c5a197e1587..58bc28d9cef2 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -68,7 +68,7 @@ extern struct tvec_base boot_tvec_bases;
#define TIMER_DEFERRABLE 0x1LU
#define TIMER_IRQSAFE 0x2LU

-#define TIMER_FLAG_MASK 0x3LU
+#define TIMER_FLAG_MASK 0x7LU

#define __TIMER_INITIALIZER(_function, _expires, _data, _flags) { \
.entry = { .prev = TIMER_ENTRY_STATIC }, \

---------x--------------------x----------------------
Warning:

config: blackfin-allyesconfig (attached as .config)
reproduce:
wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross
-O ~/bin/make.cross
chmod +x ~/bin/make.cross
git checkout ca713e393c6eceb54e803df204772a3d6e6c7981
# save the attached .config to linux build tree
make.cross ARCH=blackfin

All error/warnings:

kernel/time/timer.c: In function 'init_timers':
>> kernel/time/timer.c:1648:2: error: call to '__compiletime_assert_1648' declared with attribute error: BUILD_BUG_ON failed: __alignof__(struct tvec_base) & TIMER_FLAG_MASK


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