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relay: Use per CPU constructs for the relay channel buffer pointers
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relay essentially needs to maintain a per CPU array of channel buffer
pointers but it manually creates that array.  Instead its better to use
the per CPU constructs, provided by the kernel, to allocate & access the
array of pointer to channel buffers.

Signed-off-by: Akash Goel <akash.goel@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://lkml.kernel.org/r/1470909140-25919-1-git-send-email-akash.goel@intel.com
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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@goelakas @KAGA-KOKO
goelakas authored and KAGA-KOKO committed Sep 6, 2016
1 parent ee1e714 commit 017c59c
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Showing 2 changed files with 52 additions and 39 deletions.
17 changes: 10 additions & 7 deletions include/linux/relay.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@
#include <linux/fs.h>
#include <linux/poll.h>
#include <linux/kref.h>
#include <linux/percpu.h>

/*
* Tracks changes to rchan/rchan_buf structs
Expand Down Expand Up @@ -63,7 +64,7 @@ struct rchan
struct kref kref; /* channel refcount */
void *private_data; /* for user-defined data */
size_t last_toobig; /* tried to log event > subbuf size */
struct rchan_buf *buf[NR_CPUS]; /* per-cpu channel buffers */
struct rchan_buf ** __percpu buf; /* per-cpu channel buffers */
int is_global; /* One global buffer ? */
struct list_head list; /* for channel list */
struct dentry *parent; /* parent dentry passed to open */
Expand Down Expand Up @@ -204,7 +205,7 @@ static inline void relay_write(struct rchan *chan,
struct rchan_buf *buf;

local_irq_save(flags);
buf = chan->buf[smp_processor_id()];
buf = *this_cpu_ptr(chan->buf);
if (unlikely(buf->offset + length > chan->subbuf_size))
length = relay_switch_subbuf(buf, length);
memcpy(buf->data + buf->offset, data, length);
Expand All @@ -230,12 +231,12 @@ static inline void __relay_write(struct rchan *chan,
{
struct rchan_buf *buf;

buf = chan->buf[get_cpu()];
buf = *get_cpu_ptr(chan->buf);
if (unlikely(buf->offset + length > buf->chan->subbuf_size))
length = relay_switch_subbuf(buf, length);
memcpy(buf->data + buf->offset, data, length);
buf->offset += length;
put_cpu();
put_cpu_ptr(chan->buf);
}

/**
Expand All @@ -251,17 +252,19 @@ static inline void __relay_write(struct rchan *chan,
*/
static inline void *relay_reserve(struct rchan *chan, size_t length)
{
void *reserved;
struct rchan_buf *buf = chan->buf[smp_processor_id()];
void *reserved = NULL;
struct rchan_buf *buf = *get_cpu_ptr(chan->buf);

if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
length = relay_switch_subbuf(buf, length);
if (!length)
return NULL;
goto end;
}
reserved = buf->data + buf->offset;
buf->offset += length;

end:
put_cpu_ptr(chan->buf);
return reserved;
}

Expand Down
74 changes: 42 additions & 32 deletions kernel/relay.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -214,7 +214,7 @@ static void relay_destroy_buf(struct rchan_buf *buf)
__free_page(buf->page_array[i]);
relay_free_page_array(buf->page_array);
}
chan->buf[buf->cpu] = NULL;
*per_cpu_ptr(chan->buf, buf->cpu) = NULL;
kfree(buf->padding);
kfree(buf);
kref_put(&chan->kref, relay_destroy_channel);
Expand Down Expand Up @@ -382,20 +382,21 @@ static void __relay_reset(struct rchan_buf *buf, unsigned int init)
*/
void relay_reset(struct rchan *chan)
{
struct rchan_buf *buf;
unsigned int i;

if (!chan)
return;

if (chan->is_global && chan->buf[0]) {
__relay_reset(chan->buf[0], 0);
if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0))) {
__relay_reset(buf, 0);
return;
}

mutex_lock(&relay_channels_mutex);
for_each_possible_cpu(i)
if (chan->buf[i])
__relay_reset(chan->buf[i], 0);
if ((buf = *per_cpu_ptr(chan->buf, i)))
__relay_reset(buf, 0);
mutex_unlock(&relay_channels_mutex);
}
EXPORT_SYMBOL_GPL(relay_reset);
Expand Down Expand Up @@ -440,7 +441,7 @@ static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
struct dentry *dentry;

if (chan->is_global)
return chan->buf[0];
return *per_cpu_ptr(chan->buf, 0);

buf = relay_create_buf(chan);
if (!buf)
Expand All @@ -464,7 +465,7 @@ static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
__relay_reset(buf, 1);

if(chan->is_global) {
chan->buf[0] = buf;
*per_cpu_ptr(chan->buf, 0) = buf;
buf->cpu = 0;
}

Expand Down Expand Up @@ -526,22 +527,24 @@ static int relay_hotcpu_callback(struct notifier_block *nb,
{
unsigned int hotcpu = (unsigned long)hcpu;
struct rchan *chan;
struct rchan_buf *buf;

switch(action) {
case CPU_UP_PREPARE:
case CPU_UP_PREPARE_FROZEN:
mutex_lock(&relay_channels_mutex);
list_for_each_entry(chan, &relay_channels, list) {
if (chan->buf[hotcpu])
if ((buf = *per_cpu_ptr(chan->buf, hotcpu)))
continue;
chan->buf[hotcpu] = relay_open_buf(chan, hotcpu);
if(!chan->buf[hotcpu]) {
buf = relay_open_buf(chan, hotcpu);
if (!buf) {
printk(KERN_ERR
"relay_hotcpu_callback: cpu %d buffer "
"creation failed\n", hotcpu);
mutex_unlock(&relay_channels_mutex);
return notifier_from_errno(-ENOMEM);
}
*per_cpu_ptr(chan->buf, hotcpu) = buf;
}
mutex_unlock(&relay_channels_mutex);
break;
Expand Down Expand Up @@ -583,6 +586,7 @@ struct rchan *relay_open(const char *base_filename,
{
unsigned int i;
struct rchan *chan;
struct rchan_buf *buf;

if (!(subbuf_size && n_subbufs))
return NULL;
Expand All @@ -593,6 +597,7 @@ struct rchan *relay_open(const char *base_filename,
if (!chan)
return NULL;

chan->buf = alloc_percpu(struct rchan_buf *);
chan->version = RELAYFS_CHANNEL_VERSION;
chan->n_subbufs = n_subbufs;
chan->subbuf_size = subbuf_size;
Expand All @@ -608,9 +613,10 @@ struct rchan *relay_open(const char *base_filename,

mutex_lock(&relay_channels_mutex);
for_each_online_cpu(i) {
chan->buf[i] = relay_open_buf(chan, i);
if (!chan->buf[i])
buf = relay_open_buf(chan, i);
if (!buf)
goto free_bufs;
*per_cpu_ptr(chan->buf, i) = buf;
}
list_add(&chan->list, &relay_channels);
mutex_unlock(&relay_channels_mutex);
Expand All @@ -619,8 +625,8 @@ struct rchan *relay_open(const char *base_filename,

free_bufs:
for_each_possible_cpu(i) {
if (chan->buf[i])
relay_close_buf(chan->buf[i]);
if ((buf = *per_cpu_ptr(chan->buf, i)))
relay_close_buf(buf);
}

kref_put(&chan->kref, relay_destroy_channel);
Expand Down Expand Up @@ -666,6 +672,7 @@ int relay_late_setup_files(struct rchan *chan,
unsigned int i, curr_cpu;
unsigned long flags;
struct dentry *dentry;
struct rchan_buf *buf;
struct rchan_percpu_buf_dispatcher disp;

if (!chan || !base_filename)
Expand All @@ -684,10 +691,11 @@ int relay_late_setup_files(struct rchan *chan,

if (chan->is_global) {
err = -EINVAL;
if (!WARN_ON_ONCE(!chan->buf[0])) {
dentry = relay_create_buf_file(chan, chan->buf[0], 0);
buf = *per_cpu_ptr(chan->buf, 0);
if (!WARN_ON_ONCE(!buf)) {
dentry = relay_create_buf_file(chan, buf, 0);
if (dentry && !WARN_ON_ONCE(!chan->is_global)) {
relay_set_buf_dentry(chan->buf[0], dentry);
relay_set_buf_dentry(buf, dentry);
err = 0;
}
}
Expand All @@ -702,24 +710,25 @@ int relay_late_setup_files(struct rchan *chan,
* on all currently online CPUs.
*/
for_each_online_cpu(i) {
if (unlikely(!chan->buf[i])) {
buf = *per_cpu_ptr(chan->buf, i);
if (unlikely(!buf)) {
WARN_ONCE(1, KERN_ERR "CPU has no buffer!\n");
err = -EINVAL;
break;
}

dentry = relay_create_buf_file(chan, chan->buf[i], i);
dentry = relay_create_buf_file(chan, buf, i);
if (unlikely(!dentry)) {
err = -EINVAL;
break;
}

if (curr_cpu == i) {
local_irq_save(flags);
relay_set_buf_dentry(chan->buf[i], dentry);
relay_set_buf_dentry(buf, dentry);
local_irq_restore(flags);
} else {
disp.buf = chan->buf[i];
disp.buf = buf;
disp.dentry = dentry;
smp_mb();
/* relay_channels_mutex must be held, so wait. */
Expand Down Expand Up @@ -822,11 +831,10 @@ void relay_subbufs_consumed(struct rchan *chan,
if (!chan)
return;

if (cpu >= NR_CPUS || !chan->buf[cpu] ||
subbufs_consumed > chan->n_subbufs)
buf = *per_cpu_ptr(chan->buf, cpu);
if (cpu >= NR_CPUS || !buf || subbufs_consumed > chan->n_subbufs)
return;

buf = chan->buf[cpu];
if (subbufs_consumed > buf->subbufs_produced - buf->subbufs_consumed)
buf->subbufs_consumed = buf->subbufs_produced;
else
Expand All @@ -842,18 +850,19 @@ EXPORT_SYMBOL_GPL(relay_subbufs_consumed);
*/
void relay_close(struct rchan *chan)
{
struct rchan_buf *buf;
unsigned int i;

if (!chan)
return;

mutex_lock(&relay_channels_mutex);
if (chan->is_global && chan->buf[0])
relay_close_buf(chan->buf[0]);
if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0)))
relay_close_buf(buf);
else
for_each_possible_cpu(i)
if (chan->buf[i])
relay_close_buf(chan->buf[i]);
if ((buf = *per_cpu_ptr(chan->buf, i)))
relay_close_buf(buf);

if (chan->last_toobig)
printk(KERN_WARNING "relay: one or more items not logged "
Expand All @@ -874,20 +883,21 @@ EXPORT_SYMBOL_GPL(relay_close);
*/
void relay_flush(struct rchan *chan)
{
struct rchan_buf *buf;
unsigned int i;

if (!chan)
return;

if (chan->is_global && chan->buf[0]) {
relay_switch_subbuf(chan->buf[0], 0);
if (chan->is_global && (buf = *per_cpu_ptr(chan->buf, 0))) {
relay_switch_subbuf(buf, 0);
return;
}

mutex_lock(&relay_channels_mutex);
for_each_possible_cpu(i)
if (chan->buf[i])
relay_switch_subbuf(chan->buf[i], 0);
if ((buf = *per_cpu_ptr(chan->buf, i)))
relay_switch_subbuf(buf, 0);
mutex_unlock(&relay_channels_mutex);
}
EXPORT_SYMBOL_GPL(relay_flush);
Expand Down

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