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* [PATCH v2] elf: Use C11 atomics on _dl_mcount
@ 2022-09-05 19:14 Adhemerval Zanella
  2022-09-05 19:50 ` H.J. Lu
  0 siblings, 1 reply; 3+ messages in thread
From: Adhemerval Zanella @ 2022-09-05 19:14 UTC (permalink / raw)
  To: libc-alpha, Wilco Dijkstra

All atomic operation are counters, so relaxed MO should be suffice.

Checked on x86_64-linux-gnu.
---
 elf/dl-profile.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/elf/dl-profile.c b/elf/dl-profile.c
index ec57e3a965..67a356bf66 100644
--- a/elf/dl-profile.c
+++ b/elf/dl-profile.c
@@ -548,7 +548,7 @@ _dl_mcount (ElfW(Addr) frompc, ElfW(Addr) selfpc)
 	      size_t newfromidx;
 	      to_index = (data[narcs].self_pc
 			  / (HASHFRACTION * sizeof (*tos)));
-	      newfromidx = catomic_exchange_and_add (&fromidx, 1) + 1;
+	      newfromidx = atomic_fetch_add_relaxed (&fromidx, 1) + 1;
 	      froms[newfromidx].here = &data[narcs];
 	      froms[newfromidx].link = tos[to_index];
 	      tos[to_index] = newfromidx;
@@ -558,14 +558,14 @@ _dl_mcount (ElfW(Addr) frompc, ElfW(Addr) selfpc)
 	  /* If we still have no entry stop searching and insert.  */
 	  if (*topcindex == 0)
 	    {
-	      unsigned int newarc = catomic_exchange_and_add (narcsp, 1);
+	      unsigned int newarc = atomic_fetch_add_relaxed (narcsp, 1) + 1;
 
 	      /* In rare cases it could happen that all entries in FROMS are
 		 occupied.  So we cannot count this anymore.  */
 	      if (newarc >= fromlimit)
 		goto done;
 
-	      *topcindex = catomic_exchange_and_add (&fromidx, 1) + 1;
+	      *topcindex = atomic_fetch_add_acquire (&fromidx, 1) + 1;
 	      fromp = &froms[*topcindex];
 
 	      fromp->here = &data[newarc];
@@ -573,7 +573,7 @@ _dl_mcount (ElfW(Addr) frompc, ElfW(Addr) selfpc)
 	      data[newarc].self_pc = selfpc;
 	      data[newarc].count = 0;
 	      fromp->link = 0;
-	      catomic_increment (&narcs);
+	      atomic_fetch_add_relaxed (&narcs, 1);
 
 	      break;
 	    }
@@ -586,7 +586,7 @@ _dl_mcount (ElfW(Addr) frompc, ElfW(Addr) selfpc)
     }
 
   /* Increment the counter.  */
-  catomic_increment (&fromp->here->count);
+  atomic_fetch_add_relaxed (&fromp->here->count, 1);
 
  done:
   ;
-- 
2.34.1


^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH v2] elf: Use C11 atomics on _dl_mcount
  2022-09-05 19:14 [PATCH v2] elf: Use C11 atomics on _dl_mcount Adhemerval Zanella
@ 2022-09-05 19:50 ` H.J. Lu
  2022-09-06 10:22   ` Wilco Dijkstra
  0 siblings, 1 reply; 3+ messages in thread
From: H.J. Lu @ 2022-09-05 19:50 UTC (permalink / raw)
  To: Adhemerval Zanella; +Cc: libc-alpha, Wilco Dijkstra

On Mon, Sep 5, 2022 at 12:14 PM Adhemerval Zanella via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> All atomic operation are counters, so relaxed MO should be suffice.
>
> Checked on x86_64-linux-gnu.
> ---
>  elf/dl-profile.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/elf/dl-profile.c b/elf/dl-profile.c
> index ec57e3a965..67a356bf66 100644
> --- a/elf/dl-profile.c
> +++ b/elf/dl-profile.c
> @@ -548,7 +548,7 @@ _dl_mcount (ElfW(Addr) frompc, ElfW(Addr) selfpc)
>               size_t newfromidx;
>               to_index = (data[narcs].self_pc
>                           / (HASHFRACTION * sizeof (*tos)));
> -             newfromidx = catomic_exchange_and_add (&fromidx, 1) + 1;
> +             newfromidx = atomic_fetch_add_relaxed (&fromidx, 1) + 1;
>               froms[newfromidx].here = &data[narcs];
>               froms[newfromidx].link = tos[to_index];
>               tos[to_index] = newfromidx;
> @@ -558,14 +558,14 @@ _dl_mcount (ElfW(Addr) frompc, ElfW(Addr) selfpc)
>           /* If we still have no entry stop searching and insert.  */
>           if (*topcindex == 0)
>             {
> -             unsigned int newarc = catomic_exchange_and_add (narcsp, 1);
> +             unsigned int newarc = atomic_fetch_add_relaxed (narcsp, 1) + 1;

Shouldn't it be

unsigned int newarc = atomic_fetch_add_relaxed (narcsp, 1);

>
>               /* In rare cases it could happen that all entries in FROMS are
>                  occupied.  So we cannot count this anymore.  */
>               if (newarc >= fromlimit)
>                 goto done;
>
> -             *topcindex = catomic_exchange_and_add (&fromidx, 1) + 1;
> +             *topcindex = atomic_fetch_add_acquire (&fromidx, 1) + 1;
>               fromp = &froms[*topcindex];
>
>               fromp->here = &data[newarc];
> @@ -573,7 +573,7 @@ _dl_mcount (ElfW(Addr) frompc, ElfW(Addr) selfpc)
>               data[newarc].self_pc = selfpc;
>               data[newarc].count = 0;
>               fromp->link = 0;
> -             catomic_increment (&narcs);
> +             atomic_fetch_add_relaxed (&narcs, 1);
>
>               break;
>             }
> @@ -586,7 +586,7 @@ _dl_mcount (ElfW(Addr) frompc, ElfW(Addr) selfpc)
>      }
>
>    /* Increment the counter.  */
> -  catomic_increment (&fromp->here->count);
> +  atomic_fetch_add_relaxed (&fromp->here->count, 1);
>
>   done:
>    ;
> --
> 2.34.1
>


-- 
H.J.

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH v2] elf: Use C11 atomics on _dl_mcount
  2022-09-05 19:50 ` H.J. Lu
@ 2022-09-06 10:22   ` Wilco Dijkstra
  0 siblings, 0 replies; 3+ messages in thread
From: Wilco Dijkstra @ 2022-09-06 10:22 UTC (permalink / raw)
  To: H.J. Lu, Adhemerval Zanella; +Cc: libc-alpha

Hi,

On Mon, Sep 5, 2022 at 12:14 PM Adhemerval Zanella via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> All atomic operation are counters, so relaxed MO should be suffice.
>
> Checked on x86_64-linux-gnu.
> ---
>  elf/dl-profile.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/elf/dl-profile.c b/elf/dl-profile.c
> index ec57e3a965..67a356bf66 100644
> --- a/elf/dl-profile.c
> +++ b/elf/dl-profile.c
> @@ -548,7 +548,7 @@ _dl_mcount (ElfW(Addr) frompc, ElfW(Addr) selfpc)
>               size_t newfromidx;
>               to_index = (data[narcs].self_pc
>                           / (HASHFRACTION * sizeof (*tos)));
> -             newfromidx = catomic_exchange_and_add (&fromidx, 1) + 1;
> +             newfromidx = atomic_fetch_add_relaxed (&fromidx, 1) + 1;
>               froms[newfromidx].here = &data[narcs];
>               froms[newfromidx].link = tos[to_index];
>               tos[to_index] = newfromidx;
> @@ -558,14 +558,14 @@ _dl_mcount (ElfW(Addr) frompc, ElfW(Addr) selfpc)
>           /* If we still have no entry stop searching and insert.  */
>           if (*topcindex == 0)
>             {
> -             unsigned int newarc = catomic_exchange_and_add (narcsp, 1);
> +             unsigned int newarc = atomic_fetch_add_relaxed (narcsp, 1) + 1;

> Shouldn't it be
>
> unsigned int newarc = atomic_fetch_add_relaxed (narcsp, 1);

Indeed.

>
>               /* In rare cases it could happen that all entries in FROMS are
>                  occupied.  So we cannot count this anymore.  */
>               if (newarc >= fromlimit)
>                 goto done;
>
> -             *topcindex = catomic_exchange_and_add (&fromidx, 1) + 1;
> +             *topcindex = atomic_fetch_add_acquire (&fromidx, 1) + 1;

And this still uses acquire.

Btw it would seem easier and less error prone to split the patches from my
atomics v3 patch - that has already been fully tested.

Cheers,
Wilco

^ permalink raw reply	[flat|nested] 3+ messages in thread

end of thread, other threads:[~2022-09-06 10:22 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2022-09-05 19:14 [PATCH v2] elf: Use C11 atomics on _dl_mcount Adhemerval Zanella
2022-09-05 19:50 ` H.J. Lu
2022-09-06 10:22   ` Wilco Dijkstra

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