[PATCH lttng-ust 2/2] Fix: cache the result of getpid() internally

[PATCH lttng-ust 2/2] Fix: cache the result of getpid() internally

[Michael Jeanson]

On Linux we called getpid() directly on each tracepoint and relied on
the glibc pid cache. However, in glibc 2.25, released on 2017-02-05, the
pid cache was removed which results in a getpid syscall on each event
when the vpid context is enabled.

Remove the Linux specific case and use our internal cache all the time.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
---
 liblttng-ust/lttng-context-vpid.c | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/liblttng-ust/lttng-context-vpid.c b/liblttng-ust/lttng-context-vpid.c
index 5e5ed14..53fb314 100644
--- a/liblttng-ust/lttng-context-vpid.c
+++ b/liblttng-ust/lttng-context-vpid.c
@@ -27,17 +27,6 @@
 #include <lttng/ust-tracer.h>
 #include <lttng/ringbuffer-config.h>
 
-#ifdef __linux__
-static inline
-pid_t wrapper_getpid(void)
-{
-	return getpid();
-}
-
-void lttng_context_vpid_reset(void)
-{
-}
-#else
 /*
  * We cache the result to ensure we don't trigger a system call for
  * each event.
@@ -60,7 +49,6 @@ void lttng_context_vpid_reset(void)
 {
 	cached_vpid = 0;
 }
-#endif
 
 static
 size_t vpid_get_size(struct lttng_ctx_field *field, size_t offset)
-- 
2.7.4

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Re: [PATCH lttng-ust 1/2] Fix: reset cached vpid context on fork

[Mathieu Desnoyers]

Both patches merged into master, 2.10, 2.9, thanks!

Mathieu

----- On Mar 2, 2018, at 5:36 PM, Michael Jeanson mjeanson@efficios.com wrote:

> We currently reset the cached vtid on fork but not the vpid. This is not
> a problem on Linux because we don't cache the vpid internally but call
> getpid() directly and rely on the glibc pid cache.
> 
> Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
> ---
> liblttng-ust/lttng-ust-comm.c | 1 +
> 1 file changed, 1 insertion(+)
> 
> diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
> index 4391446..d4add1c 100644
> --- a/liblttng-ust/lttng-ust-comm.c
> +++ b/liblttng-ust/lttng-ust-comm.c
> @@ -2011,6 +2011,7 @@ void ust_after_fork_child(sigset_t *restore_sigset)
> {
> 	if (URCU_TLS(lttng_ust_nest_count))
> 		return;
> +	lttng_context_vpid_reset();
> 	lttng_context_vtid_reset();
> 	DBG("process %d", getpid());
> 	/* Release urcu mutexes */
> --
> 2.7.4

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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