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SubjectRe: [PATCH v3 4/9] x86/mm/tlb: Flush remote and local TLBs concurrently
On Thu, Jul 18, 2019 at 05:58:32PM -0700, Nadav Amit wrote:
> @@ -709,8 +716,9 @@ void native_flush_tlb_others(const struct cpumask *cpumask,
> * doing a speculative memory access.
> */
> if (info->freed_tables) {
> - smp_call_function_many(cpumask, flush_tlb_func_remote,
> - (void *)info, 1);
> + __smp_call_function_many(cpumask, flush_tlb_func_remote,
> + flush_tlb_func_local,
> + (void *)info, 1);
> } else {
> /*
> * Although we could have used on_each_cpu_cond_mask(),
> @@ -737,7 +745,8 @@ void native_flush_tlb_others(const struct cpumask *cpumask,
> if (tlb_is_not_lazy(cpu))
> __cpumask_set_cpu(cpu, cond_cpumask);
> }
> - smp_call_function_many(cond_cpumask, flush_tlb_func_remote,
> + __smp_call_function_many(cond_cpumask, flush_tlb_func_remote,
> + flush_tlb_func_local,
> (void *)info, 1);
> }
> }

Do we really need that _local/_remote distinction? ISTR you had a patch
that frobbed flush_tlb_info into the csd and that gave space
constraints, but I'm not seeing that here (probably a wise, get stuff
merged etc..).

struct __call_single_data {
struct llist_node llist; /* 0 8 */
smp_call_func_t func; /* 8 8 */
void * info; /* 16 8 */
unsigned int flags; /* 24 4 */

/* size: 32, cachelines: 1, members: 4 */
/* padding: 4 */
/* last cacheline: 32 bytes */
};

struct flush_tlb_info {
struct mm_struct * mm; /* 0 8 */
long unsigned int start; /* 8 8 */
long unsigned int end; /* 16 8 */
u64 new_tlb_gen; /* 24 8 */
unsigned int stride_shift; /* 32 4 */
bool freed_tables; /* 36 1 */

/* size: 40, cachelines: 1, members: 6 */
/* padding: 3 */
/* last cacheline: 40 bytes */
};

IIRC what you did was make void *__call_single_data::info the last
member and a union until the full cacheline size (64). Given the above
that would get us 24 bytes for csd, leaving us 40 for that
flush_tlb_info.

But then we can still do something like the below, which doesn't change
things and still gets rid of that dual function crud, simplifying
smp_call_function_many again.

Index: linux-2.6/arch/x86/include/asm/tlbflush.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/tlbflush.h
+++ linux-2.6/arch/x86/include/asm/tlbflush.h
@@ -546,8 +546,9 @@ struct flush_tlb_info {
unsigned long start;
unsigned long end;
u64 new_tlb_gen;
- unsigned int stride_shift;
- bool freed_tables;
+ unsigned int cpu;
+ unsigned short stride_shift;
+ unsigned char freed_tables;
};

#define local_flush_tlb() __flush_tlb()
Index: linux-2.6/arch/x86/mm/tlb.c
===================================================================
--- linux-2.6.orig/arch/x86/mm/tlb.c
+++ linux-2.6/arch/x86/mm/tlb.c
@@ -659,6 +659,27 @@ static void flush_tlb_func_remote(void *
flush_tlb_func_common(f, false, TLB_REMOTE_SHOOTDOWN);
}

+static void flush_tlb_func(void *info)
+{
+ const struct flush_tlb_info *f = info;
+ enum tlb_flush_reason reason = TLB_REMOTE_SHOOTDOWN;
+ bool local = false;
+
+ if (f->cpu == smp_processor_id()) {
+ local = true;
+ reason = (f->mm == NULL) ? TLB_LOCAL_SHOOTDOWN : TLB_LOCAL_MM_SHOOTDOWN;
+ } else {
+ inc_irq_stat(irq_tlb_count);
+
+ if (f->mm && f->mm != this_cpu_read(cpu_tlbstate.loaded_mm))
+ return;
+
+ count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
+ }
+
+ flush_tlb_func_common(f, local, reason);
+}
+
static bool tlb_is_not_lazy(int cpu)
{
return !per_cpu(cpu_tlbstate_shared.is_lazy, cpu);
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