[PATCH v5 3/4] riscv: Make __flush_tlb_range() loop over pte instead of flushing the whole tlb
From: Alexandre Ghiti
Date: Thu Oct 19 2023 - 10:05:25 EST
Currently, when the range to flush covers more than one page (a 4K page or
a hugepage), __flush_tlb_range() flushes the whole tlb. Flushing the whole
tlb comes with a greater cost than flushing a single entry so we should
flush single entries up to a certain threshold so that:
threshold * cost of flushing a single entry < cost of flushing the whole
tlb.
Co-developed-by: Mayuresh Chitale <mchitale@xxxxxxxxxxxxxxxx>
Signed-off-by: Mayuresh Chitale <mchitale@xxxxxxxxxxxxxxxx>
Signed-off-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx> # On RZ/Five SMARC
---
arch/riscv/include/asm/sbi.h | 3 -
arch/riscv/include/asm/tlbflush.h | 3 +
arch/riscv/kernel/sbi.c | 32 +++------
arch/riscv/mm/tlbflush.c | 115 +++++++++++++++---------------
4 files changed, 72 insertions(+), 81 deletions(-)
diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
index 12dfda6bb924..0892f4421bc4 100644
--- a/arch/riscv/include/asm/sbi.h
+++ b/arch/riscv/include/asm/sbi.h
@@ -280,9 +280,6 @@ void sbi_set_timer(uint64_t stime_value);
void sbi_shutdown(void);
void sbi_send_ipi(unsigned int cpu);
int sbi_remote_fence_i(const struct cpumask *cpu_mask);
-int sbi_remote_sfence_vma(const struct cpumask *cpu_mask,
- unsigned long start,
- unsigned long size);
int sbi_remote_sfence_vma_asid(const struct cpumask *cpu_mask,
unsigned long start,
diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
index f5c4fb0ae642..170a49c531c6 100644
--- a/arch/riscv/include/asm/tlbflush.h
+++ b/arch/riscv/include/asm/tlbflush.h
@@ -11,6 +11,9 @@
#include <asm/smp.h>
#include <asm/errata_list.h>
+#define FLUSH_TLB_MAX_SIZE ((unsigned long)-1)
+#define FLUSH_TLB_NO_ASID ((unsigned long)-1)
+
#ifdef CONFIG_MMU
extern unsigned long asid_mask;
diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
index c672c8ba9a2a..5a62ed1da453 100644
--- a/arch/riscv/kernel/sbi.c
+++ b/arch/riscv/kernel/sbi.c
@@ -11,6 +11,7 @@
#include <linux/reboot.h>
#include <asm/sbi.h>
#include <asm/smp.h>
+#include <asm/tlbflush.h>
/* default SBI version is 0.1 */
unsigned long sbi_spec_version __ro_after_init = SBI_SPEC_VERSION_DEFAULT;
@@ -376,32 +377,15 @@ int sbi_remote_fence_i(const struct cpumask *cpu_mask)
}
EXPORT_SYMBOL(sbi_remote_fence_i);
-/**
- * sbi_remote_sfence_vma() - Execute SFENCE.VMA instructions on given remote
- * harts for the specified virtual address range.
- * @cpu_mask: A cpu mask containing all the target harts.
- * @start: Start of the virtual address
- * @size: Total size of the virtual address range.
- *
- * Return: 0 on success, appropriate linux error code otherwise.
- */
-int sbi_remote_sfence_vma(const struct cpumask *cpu_mask,
- unsigned long start,
- unsigned long size)
-{
- return __sbi_rfence(SBI_EXT_RFENCE_REMOTE_SFENCE_VMA,
- cpu_mask, start, size, 0, 0);
-}
-EXPORT_SYMBOL(sbi_remote_sfence_vma);
-
/**
* sbi_remote_sfence_vma_asid() - Execute SFENCE.VMA instructions on given
- * remote harts for a virtual address range belonging to a specific ASID.
+ * remote harts for a virtual address range belonging to a specific ASID or not.
*
* @cpu_mask: A cpu mask containing all the target harts.
* @start: Start of the virtual address
* @size: Total size of the virtual address range.
- * @asid: The value of address space identifier (ASID).
+ * @asid: The value of address space identifier (ASID), or FLUSH_TLB_NO_ASID
+ * for flushing all address spaces.
*
* Return: 0 on success, appropriate linux error code otherwise.
*/
@@ -410,8 +394,12 @@ int sbi_remote_sfence_vma_asid(const struct cpumask *cpu_mask,
unsigned long size,
unsigned long asid)
{
- return __sbi_rfence(SBI_EXT_RFENCE_REMOTE_SFENCE_VMA_ASID,
- cpu_mask, start, size, asid, 0);
+ if (asid == FLUSH_TLB_NO_ASID)
+ return __sbi_rfence(SBI_EXT_RFENCE_REMOTE_SFENCE_VMA,
+ cpu_mask, start, size, 0, 0);
+ else
+ return __sbi_rfence(SBI_EXT_RFENCE_REMOTE_SFENCE_VMA_ASID,
+ cpu_mask, start, size, asid, 0);
}
EXPORT_SYMBOL(sbi_remote_sfence_vma_asid);
diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index 5933744df91a..c27ba720e35f 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -9,28 +9,50 @@
static inline void local_flush_tlb_all_asid(unsigned long asid)
{
- __asm__ __volatile__ ("sfence.vma x0, %0"
- :
- : "r" (asid)
- : "memory");
+ if (asid != FLUSH_TLB_NO_ASID)
+ __asm__ __volatile__ ("sfence.vma x0, %0"
+ :
+ : "r" (asid)
+ : "memory");
+ else
+ local_flush_tlb_all();
}
static inline void local_flush_tlb_page_asid(unsigned long addr,
unsigned long asid)
{
- __asm__ __volatile__ ("sfence.vma %0, %1"
- :
- : "r" (addr), "r" (asid)
- : "memory");
+ if (asid != FLUSH_TLB_NO_ASID)
+ __asm__ __volatile__ ("sfence.vma %0, %1"
+ :
+ : "r" (addr), "r" (asid)
+ : "memory");
+ else
+ local_flush_tlb_page(addr);
}
-static inline void local_flush_tlb_range(unsigned long start,
- unsigned long size, unsigned long stride)
+/*
+ * Flush entire TLB if number of entries to be flushed is greater
+ * than the threshold below.
+ */
+static unsigned long tlb_flush_all_threshold __read_mostly = 64;
+
+static void local_flush_tlb_range_threshold_asid(unsigned long start,
+ unsigned long size,
+ unsigned long stride,
+ unsigned long asid)
{
- if (size <= stride)
- local_flush_tlb_page(start);
- else
- local_flush_tlb_all();
+ u16 nr_ptes_in_range = DIV_ROUND_UP(size, stride);
+ int i;
+
+ if (nr_ptes_in_range > tlb_flush_all_threshold) {
+ local_flush_tlb_all_asid(asid);
+ return;
+ }
+
+ for (i = 0; i < nr_ptes_in_range; ++i) {
+ local_flush_tlb_page_asid(start, asid);
+ start += stride;
+ }
}
static inline void local_flush_tlb_range_asid(unsigned long start,
@@ -38,8 +60,10 @@ static inline void local_flush_tlb_range_asid(unsigned long start,
{
if (size <= stride)
local_flush_tlb_page_asid(start, asid);
- else
+ else if (size == FLUSH_TLB_MAX_SIZE)
local_flush_tlb_all_asid(asid);
+ else
+ local_flush_tlb_range_threshold_asid(start, size, stride, asid);
}
static void __ipi_flush_tlb_all(void *info)
@@ -52,7 +76,7 @@ void flush_tlb_all(void)
if (riscv_use_ipi_for_rfence())
on_each_cpu(__ipi_flush_tlb_all, NULL, 1);
else
- sbi_remote_sfence_vma(NULL, 0, -1);
+ sbi_remote_sfence_vma_asid(NULL, 0, FLUSH_TLB_MAX_SIZE, FLUSH_TLB_NO_ASID);
}
struct flush_tlb_range_data {
@@ -69,18 +93,12 @@ static void __ipi_flush_tlb_range_asid(void *info)
local_flush_tlb_range_asid(d->start, d->size, d->stride, d->asid);
}
-static void __ipi_flush_tlb_range(void *info)
-{
- struct flush_tlb_range_data *d = info;
-
- local_flush_tlb_range(d->start, d->size, d->stride);
-}
-
static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
unsigned long size, unsigned long stride)
{
struct flush_tlb_range_data ftd;
struct cpumask *cmask = mm_cpumask(mm);
+ unsigned long asid = FLUSH_TLB_NO_ASID;
unsigned int cpuid;
bool broadcast;
@@ -90,39 +108,24 @@ static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
cpuid = get_cpu();
/* check if the tlbflush needs to be sent to other CPUs */
broadcast = cpumask_any_but(cmask, cpuid) < nr_cpu_ids;
- if (static_branch_unlikely(&use_asid_allocator)) {
- unsigned long asid = atomic_long_read(&mm->context.id) & asid_mask;
-
- if (broadcast) {
- if (riscv_use_ipi_for_rfence()) {
- ftd.asid = asid;
- ftd.start = start;
- ftd.size = size;
- ftd.stride = stride;
- on_each_cpu_mask(cmask,
- __ipi_flush_tlb_range_asid,
- &ftd, 1);
- } else
- sbi_remote_sfence_vma_asid(cmask,
- start, size, asid);
- } else {
- local_flush_tlb_range_asid(start, size, stride, asid);
- }
+
+ if (static_branch_unlikely(&use_asid_allocator))
+ asid = atomic_long_read(&mm->context.id) & asid_mask;
+
+ if (broadcast) {
+ if (riscv_use_ipi_for_rfence()) {
+ ftd.asid = asid;
+ ftd.start = start;
+ ftd.size = size;
+ ftd.stride = stride;
+ on_each_cpu_mask(cmask,
+ __ipi_flush_tlb_range_asid,
+ &ftd, 1);
+ } else
+ sbi_remote_sfence_vma_asid(cmask,
+ start, size, asid);
} else {
- if (broadcast) {
- if (riscv_use_ipi_for_rfence()) {
- ftd.asid = 0;
- ftd.start = start;
- ftd.size = size;
- ftd.stride = stride;
- on_each_cpu_mask(cmask,
- __ipi_flush_tlb_range,
- &ftd, 1);
- } else
- sbi_remote_sfence_vma(cmask, start, size);
- } else {
- local_flush_tlb_range(start, size, stride);
- }
+ local_flush_tlb_range_asid(start, size, stride, asid);
}
put_cpu();
@@ -130,7 +133,7 @@ static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
void flush_tlb_mm(struct mm_struct *mm)
{
- __flush_tlb_range(mm, 0, -1, PAGE_SIZE);
+ __flush_tlb_range(mm, 0, FLUSH_TLB_MAX_SIZE, PAGE_SIZE);
}
void flush_tlb_mm_range(struct mm_struct *mm,
--
2.39.2