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Date: Mon, 20 Oct 2008 11:43:19 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To: Lai Jiangshan <laijs@...fujitsu.com>
Cc: Ingo Molnar <mingo@...e.hu>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH tip/tracing/markers] markers: simplify
marker_set_format()
* Lai Jiangshan (laijs@...fujitsu.com) wrote:
> Mathieu Desnoyers wrote:
> > * Lai Jiangshan (laijs@...fujitsu.com) wrote:
> >> current marker_set_format() is complex this patch simplify it,
> >> and decrease the overhead of marker_update_probes().
> >>
> >
> > Yep, I think I did put the format string after the name \0, which was
> > rather tricky. I agree that such change makes the code more readable at
> > the expense of doing 2 allocations per marker rather than one, but
> > readability might be a good thing here.
>
> this fix did help for readability and made code cleanly.
> but it's still 1 allocation per marker_entry when format != NULL.
> the previous benefit is not lost.
>
Yes, but the common case is to have format != NULL, so it's 2 alloc per
marker. :)
Mathieu
> Thanks, Lai
>
> >
> > Thanks !
> >
> > Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> >
> >> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> >> ---
> >> diff --git a/kernel/marker.c b/kernel/marker.c
> >> index e49a9c5..ef43c86 100644
> >> --- a/kernel/marker.c
> >> +++ b/kernel/marker.c
> >> @@ -65,6 +65,7 @@ struct marker_entry {
> >> void *oldptr;
> >> int rcu_pending;
> >> unsigned char ptype:1;
> >> + unsigned char format_allocated:1;
> >> char name[0]; /* Contains name'\0'format'\0' */
> >> };
> >>
> >> @@ -415,6 +416,7 @@ static struct marker_entry *add_marker(const char *name, const char *format)
> >> e->single.probe_private = NULL;
> >> e->multi = NULL;
> >> e->ptype = 0;
> >> + e->format_allocated = 0;
> >> e->refcount = 0;
> >> e->rcu_pending = 0;
> >> hlist_add_head(&e->hlist, head);
> >> @@ -446,6 +448,8 @@ static int remove_marker(const char *name)
> >> if (e->single.func != __mark_empty_function)
> >> return -EBUSY;
> >> hlist_del(&e->hlist);
> >> + if (e->format_allocated)
> >> + kfree(e->format);
> >> /* Make sure the call_rcu has been executed */
> >> if (e->rcu_pending)
> >> rcu_barrier_sched();
> >> @@ -456,57 +460,34 @@ static int remove_marker(const char *name)
> >> /*
> >> * Set the mark_entry format to the format found in the element.
> >> */
> >> -static int marker_set_format(struct marker_entry **entry, const char *format)
> >> +static int marker_set_format(struct marker_entry *entry, const char *format)
> >> {
> >> - struct marker_entry *e;
> >> - size_t name_len = strlen((*entry)->name) + 1;
> >> - size_t format_len = strlen(format) + 1;
> >> -
> >> -
> >> - e = kmalloc(sizeof(struct marker_entry) + name_len + format_len,
> >> - GFP_KERNEL);
> >> - if (!e)
> >> + entry->format = kstrdup(format, GFP_KERNEL);
> >> + if (!entry->format)
> >> return -ENOMEM;
> >> - memcpy(&e->name[0], (*entry)->name, name_len);
> >> - e->format = &e->name[name_len];
> >> - memcpy(e->format, format, format_len);
> >> - if (strcmp(e->format, MARK_NOARGS) == 0)
> >> - e->call = marker_probe_cb_noarg;
> >> - else
> >> - e->call = marker_probe_cb;
> >> - e->single = (*entry)->single;
> >> - e->multi = (*entry)->multi;
> >> - e->ptype = (*entry)->ptype;
> >> - e->refcount = (*entry)->refcount;
> >> - e->rcu_pending = 0;
> >> - hlist_add_before(&e->hlist, &(*entry)->hlist);
> >> - hlist_del(&(*entry)->hlist);
> >> - /* Make sure the call_rcu has been executed */
> >> - if ((*entry)->rcu_pending)
> >> - rcu_barrier_sched();
> >> - kfree(*entry);
> >> - *entry = e;
> >> + entry->format_allocated = 1;
> >> +
> >> trace_mark(core_marker_format, "name %s format %s",
> >> - e->name, e->format);
> >> + entry->name, entry->format);
> >> return 0;
> >> }
> >>
> >> /*
> >> * Sets the probe callback corresponding to one marker.
> >> */
> >> -static int set_marker(struct marker_entry **entry, struct marker *elem,
> >> +static int set_marker(struct marker_entry *entry, struct marker *elem,
> >> int active)
> >> {
> >> int ret;
> >> - WARN_ON(strcmp((*entry)->name, elem->name) != 0);
> >> + WARN_ON(strcmp(entry->name, elem->name) != 0);
> >>
> >> - if ((*entry)->format) {
> >> - if (strcmp((*entry)->format, elem->format) != 0) {
> >> + if (entry->format) {
> >> + if (strcmp(entry->format, elem->format) != 0) {
> >> printk(KERN_NOTICE
> >> "Format mismatch for probe %s "
> >> "(%s), marker (%s)\n",
> >> - (*entry)->name,
> >> - (*entry)->format,
> >> + entry->name,
> >> + entry->format,
> >> elem->format);
> >> return -EPERM;
> >> }
> >> @@ -522,34 +503,33 @@ static int set_marker(struct marker_entry **entry, struct marker *elem,
> >> * pass from a "safe" callback (with argument) to an "unsafe"
> >> * callback (does not set arguments).
> >> */
> >> - elem->call = (*entry)->call;
> >> + elem->call = entry->call;
> >> /*
> >> * Sanity check :
> >> * We only update the single probe private data when the ptr is
> >> * set to a _non_ single probe! (0 -> 1 and N -> 1, N != 1)
> >> */
> >> WARN_ON(elem->single.func != __mark_empty_function
> >> - && elem->single.probe_private
> >> - != (*entry)->single.probe_private &&
> >> - !elem->ptype);
> >> - elem->single.probe_private = (*entry)->single.probe_private;
> >> + && elem->single.probe_private != entry->single.probe_private
> >> + && !elem->ptype);
> >> + elem->single.probe_private = entry->single.probe_private;
> >> /*
> >> * Make sure the private data is valid when we update the
> >> * single probe ptr.
> >> */
> >> smp_wmb();
> >> - elem->single.func = (*entry)->single.func;
> >> + elem->single.func = entry->single.func;
> >> /*
> >> * We also make sure that the new probe callbacks array is consistent
> >> * before setting a pointer to it.
> >> */
> >> - rcu_assign_pointer(elem->multi, (*entry)->multi);
> >> + rcu_assign_pointer(elem->multi, entry->multi);
> >> /*
> >> * Update the function or multi probe array pointer before setting the
> >> * ptype.
> >> */
> >> smp_wmb();
> >> - elem->ptype = (*entry)->ptype;
> >> + elem->ptype = entry->ptype;
> >> elem->state = active;
> >>
> >> return 0;
> >> @@ -593,8 +573,7 @@ void marker_update_probe_range(struct marker *begin,
> >> for (iter = begin; iter < end; iter++) {
> >> mark_entry = get_marker(iter->name);
> >> if (mark_entry) {
> >> - set_marker(&mark_entry, iter,
> >> - !!mark_entry->refcount);
> >> + set_marker(mark_entry, iter, !!mark_entry->refcount);
> >> /*
> >> * ignore error, continue
> >> */
> >> @@ -656,7 +635,7 @@ int marker_probe_register(const char *name, const char *format,
> >> ret = PTR_ERR(entry);
> >> } else if (format) {
> >> if (!entry->format)
> >> - ret = marker_set_format(&entry, format);
> >> + ret = marker_set_format(entry, format);
> >> else if (strcmp(entry->format, format))
> >> ret = -EPERM;
> >> }
> >>
> >>
> >>
> >>
> >>
> >
>
>
--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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