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Message-ID: <20191114164622.GC233237@google.com>
Date: Thu, 14 Nov 2019 11:46:22 -0500
From: Joel Fernandes <joel@...lfernandes.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, Ioannis Ilkos <ilkos@...gle.com>,
minchan@...gle.com, primiano@...gle.com, fmayer@...gle.com,
hjd@...gle.com, joaodias@...gle.com, lalitm@...gle.com,
rslawik@...gle.com, sspatil@...gle.com, timmurray@...gle.com,
Andrew Morton <akpm@...ux-foundation.org>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Changbin Du <changbin.du@...el.com>,
Ingo Molnar <mingo@...hat.com>, Joe Perches <joe@...ches.com>,
Kees Cook <keescook@...omium.org>, linux-mm@...ck.org,
Michal Hocko <mhocko@...e.com>, Petr Mladek <pmladek@...e.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
Sakari Ailus <sakari.ailus@...ux.intel.com>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH] rss_stat: Add support to detect RSS updates of external
mm
On Wed, Nov 13, 2019 at 03:38:16PM -0500, Steven Rostedt wrote:
[snip]
> > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > index dee8fc467fcf..401baaac1813 100644
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -761,11 +761,34 @@ static int __init initialize_ptr_random(void)
> > early_initcall(initialize_ptr_random);
> >
> > /* Maps a pointer to a 32 bit unique identifier. */
> > +int ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
> > +{
> > + const char *str = sizeof(ptr) == 8 ? "(____ptrval____)" : "(ptrval)";
> > + unsigned long hashval;
> > +
> > + if (static_branch_unlikely(¬_filled_random_ptr_key))
> > + return -EAGAIN;
> > +
> > +#ifdef CONFIG_64BIT
> > + hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);
> > + /*
> > + * Mask off the first 32 bits, this makes explicit that we have
> > + * modified the address (and 32 bits is plenty for a unique ID).
> > + */
> > + hashval = hashval & 0xffffffff;
> > +#else
> > + hashval = (unsigned long)siphash_1u32((u32)ptr, &ptr_key);
> > +#endif
> > + *hashval_out = hashval;
> > + return 0;
> > +}
> > +
> > static char *ptr_to_id(char *buf, char *end, const void *ptr,
> > struct printf_spec spec)
> > {
> > const char *str = sizeof(ptr) == 8 ? "(____ptrval____)" : "(ptrval)";
> > unsigned long hashval;
> > + int ret;
> >
> > /* When debugging early boot use non-cryptographically secure hash. */
> > if (unlikely(debug_boot_weak_hash)) {
> > @@ -773,22 +796,13 @@ static char *ptr_to_id(char *buf, char *end, const void *ptr,
> > return pointer_string(buf, end, (const void *)hashval, spec);
> > }
> >
> > - if (static_branch_unlikely(¬_filled_random_ptr_key)) {
> > + ret = ptr_to_hashval(ptr, &hashval);
> > + if (ret) {
>
> This is a hot path (used in trace_printk()), and you just turned a
> static_branch into a function call.
>
> Can we make a __ptr_to_hashval() static inline, and have
> ptr_to_hashval() call that, but use the static inline here, where the
> static_branch gets called directly here?
Sure, like this?
---8<-----------------------
From: Joel Fernandes <joelaf@...gle.com>
Subject: [PATCH] vsprintf: Inline call to ptr_to_hashval
There is concern that ptr_to_hashval not being inlined can cause performance
issues (unlike before where it was a static branch) with trace_printk being a
hot path for it. Just create an inline version called __ptr_to_hashval(), and
have the actual ptr_to_hashval() call it.
Link: http://lore.kernel.org/r/20191113153816.14b95acd@gandalf.local.home
Suggested-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Joel Fernandes <joelaf@...gle.com>
---
lib/vsprintf.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 405a8ca220a0..7c488a1ce318 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -761,7 +761,7 @@ static int __init initialize_ptr_random(void)
early_initcall(initialize_ptr_random);
/* Maps a pointer to a 32 bit unique identifier. */
-int ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
+static inline int __ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
{
unsigned long hashval;
@@ -782,6 +782,11 @@ int ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
return 0;
}
+int ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
+{
+ return __ptr_to_hashval(ptr, hashval_out);
+}
+
static char *ptr_to_id(char *buf, char *end, const void *ptr,
struct printf_spec spec)
{
@@ -795,7 +800,7 @@ static char *ptr_to_id(char *buf, char *end, const void *ptr,
return pointer_string(buf, end, (const void *)hashval, spec);
}
- ret = ptr_to_hashval(ptr, &hashval);
+ ret = __ptr_to_hashval(ptr, &hashval);
if (ret) {
spec.field_width = 2 * sizeof(ptr);
/* string length must be less than default_width */
--
2.24.0.rc1.363.gb1bccd3e3d-goog
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