Currently we evict an entry to the victim TLB when it doesn't match
the current address. But it could be that there's no match because
the current entry is empty (i.e. all -1's, for instance via tlb_flush).
Do not evict the entry to the vtlb in that case.

This change will help us keep track of the TLB's use rate.

Signed-off-by: Emilio G. Cota <cota@braap.org>
---
 include/exec/cpu-all.h | 9 +++++++++
 accel/tcg/cputlb.c     | 2 +-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
index 117d2fbbca..e21140049b 100644
--- a/include/exec/cpu-all.h
+++ b/include/exec/cpu-all.h
@@ -362,6 +362,15 @@ static inline bool tlb_hit(target_ulong tlb_addr, target_ulong addr)
     return tlb_hit_page(tlb_addr, addr & TARGET_PAGE_MASK);
 }
 
+/**
+ * tlb_entry_is_empty - return true if the entry is not in use
+ * @te: pointer to CPUTLBEntry
+ */
+static inline bool tlb_entry_is_empty(const CPUTLBEntry *te)
+{
+    return te->addr_read == -1 && te->addr_write == -1 && te->addr_code == -1;
+}
+
 void dump_exec_info(FILE *f, fprintf_function cpu_fprintf);
 void dump_opcount_info(FILE *f, fprintf_function cpu_fprintf);
 #endif /* !CONFIG_USER_ONLY */
diff --git a/accel/tcg/cputlb.c b/accel/tcg/cputlb.c
index 80406f1033..4dc47e603c 100644
--- a/accel/tcg/cputlb.c
+++ b/accel/tcg/cputlb.c
@@ -689,7 +689,7 @@ void tlb_set_page_with_attrs(CPUState *cpu, target_ulong vaddr,
      * Only evict the old entry to the victim tlb if it's for a
      * different page; otherwise just overwrite the stale data.
      */
-    if (!tlb_hit_page_anyprot(te, vaddr_page)) {
+    if (!tlb_hit_page_anyprot(te, vaddr_page) && !tlb_entry_is_empty(te)) {
         unsigned vidx = env->vtlb_index++ % CPU_VTLB_SIZE;
         CPUTLBEntry *tv = &env->tlb_v_table[mmu_idx][vidx];
 
-- 
2.17.1

Emilio G. Cota <cota@braap.org> writes:

> Currently we evict an entry to the victim TLB when it doesn't match
> the current address. But it could be that there's no match because
> the current entry is empty (i.e. all -1's, for instance via tlb_flush).
> Do not evict the entry to the vtlb in that case.
>
> This change will help us keep track of the TLB's use rate.
>
> Signed-off-by: Emilio G. Cota <cota@braap.org>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

> ---
>  include/exec/cpu-all.h | 9 +++++++++
>  accel/tcg/cputlb.c     | 2 +-
>  2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
> index 117d2fbbca..e21140049b 100644
> --- a/include/exec/cpu-all.h
> +++ b/include/exec/cpu-all.h
> @@ -362,6 +362,15 @@ static inline bool tlb_hit(target_ulong tlb_addr, target_ulong addr)
>      return tlb_hit_page(tlb_addr, addr & TARGET_PAGE_MASK);
>  }
>
> +/**
> + * tlb_entry_is_empty - return true if the entry is not in use
> + * @te: pointer to CPUTLBEntry
> + */
> +static inline bool tlb_entry_is_empty(const CPUTLBEntry *te)
> +{
> +    return te->addr_read == -1 && te->addr_write == -1 && te->addr_code == -1;
> +}
> +
>  void dump_exec_info(FILE *f, fprintf_function cpu_fprintf);
>  void dump_opcount_info(FILE *f, fprintf_function cpu_fprintf);
>  #endif /* !CONFIG_USER_ONLY */
> diff --git a/accel/tcg/cputlb.c b/accel/tcg/cputlb.c
> index 80406f1033..4dc47e603c 100644
> --- a/accel/tcg/cputlb.c
> +++ b/accel/tcg/cputlb.c
> @@ -689,7 +689,7 @@ void tlb_set_page_with_attrs(CPUState *cpu, target_ulong vaddr,
>       * Only evict the old entry to the victim tlb if it's for a
>       * different page; otherwise just overwrite the stale data.
>       */
> -    if (!tlb_hit_page_anyprot(te, vaddr_page)) {
> +    if (!tlb_hit_page_anyprot(te, vaddr_page) && !tlb_entry_is_empty(te)) {
>          unsigned vidx = env->vtlb_index++ % CPU_VTLB_SIZE;
>          CPUTLBEntry *tv = &env->tlb_v_table[mmu_idx][vidx];


--
Alex Bennée

On 10/8/18 4:27 PM, Emilio G. Cota wrote:
> Currently we evict an entry to the victim TLB when it doesn't match
> the current address. But it could be that there's no match because
> the current entry is empty (i.e. all -1's, for instance via tlb_flush).
> Do not evict the entry to the vtlb in that case.
> 
> This change will help us keep track of the TLB's use rate.
> 
> Signed-off-by: Emilio G. Cota <cota@braap.org>
> ---
>  include/exec/cpu-all.h | 9 +++++++++
>  accel/tcg/cputlb.c     | 2 +-
>  2 files changed, 10 insertions(+), 1 deletion(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~