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author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2009-03-25 19:39:37 +0100 |
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committer | Ingo Molnar <mingo@elte.hu> | 2009-06-18 14:46:11 +0200 |
commit | 43a21ea81a2400992561146327c4785ce7f7be38 (patch) | |
tree | d4974c0ff9d7f40291515c5c0cf7e0d51abccb66 /kernel/perf_counter.c | |
parent | d3a9262e59f7fb83c6d44df3b2b1460ed57d3ea1 (diff) | |
download | lwn-43a21ea81a2400992561146327c4785ce7f7be38.tar.gz lwn-43a21ea81a2400992561146327c4785ce7f7be38.zip |
perf_counter: Add event overlow handling
Alternative method of mmap() data output handling that provides
better overflow management and a more reliable data stream.
Unlike the previous method, that didn't have any user->kernel
feedback and relied on userspace keeping up, this method relies on
userspace writing its last read position into the control page.
It will ensure new output doesn't overwrite not-yet read events,
new events for which there is no space left are lost and the
overflow counter is incremented, providing exact event loss
numbers.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/perf_counter.c')
-rw-r--r-- | kernel/perf_counter.c | 185 |
1 files changed, 130 insertions, 55 deletions
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c index 109a95723859..7e9108efd305 100644 --- a/kernel/perf_counter.c +++ b/kernel/perf_counter.c @@ -1794,6 +1794,12 @@ static int perf_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf) struct perf_mmap_data *data; int ret = VM_FAULT_SIGBUS; + if (vmf->flags & FAULT_FLAG_MKWRITE) { + if (vmf->pgoff == 0) + ret = 0; + return ret; + } + rcu_read_lock(); data = rcu_dereference(counter->data); if (!data) @@ -1807,9 +1813,16 @@ static int perf_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf) if ((unsigned)nr > data->nr_pages) goto unlock; + if (vmf->flags & FAULT_FLAG_WRITE) + goto unlock; + vmf->page = virt_to_page(data->data_pages[nr]); } + get_page(vmf->page); + vmf->page->mapping = vma->vm_file->f_mapping; + vmf->page->index = vmf->pgoff; + ret = 0; unlock: rcu_read_unlock(); @@ -1862,6 +1875,14 @@ fail: return -ENOMEM; } +static void perf_mmap_free_page(unsigned long addr) +{ + struct page *page = virt_to_page(addr); + + page->mapping = NULL; + __free_page(page); +} + static void __perf_mmap_data_free(struct rcu_head *rcu_head) { struct perf_mmap_data *data; @@ -1869,9 +1890,10 @@ static void __perf_mmap_data_free(struct rcu_head *rcu_head) data = container_of(rcu_head, struct perf_mmap_data, rcu_head); - free_page((unsigned long)data->user_page); + perf_mmap_free_page((unsigned long)data->user_page); for (i = 0; i < data->nr_pages; i++) - free_page((unsigned long)data->data_pages[i]); + perf_mmap_free_page((unsigned long)data->data_pages[i]); + kfree(data); } @@ -1908,9 +1930,10 @@ static void perf_mmap_close(struct vm_area_struct *vma) } static struct vm_operations_struct perf_mmap_vmops = { - .open = perf_mmap_open, - .close = perf_mmap_close, - .fault = perf_mmap_fault, + .open = perf_mmap_open, + .close = perf_mmap_close, + .fault = perf_mmap_fault, + .page_mkwrite = perf_mmap_fault, }; static int perf_mmap(struct file *file, struct vm_area_struct *vma) @@ -1924,7 +1947,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma) long user_extra, extra; int ret = 0; - if (!(vma->vm_flags & VM_SHARED) || (vma->vm_flags & VM_WRITE)) + if (!(vma->vm_flags & VM_SHARED)) return -EINVAL; vma_size = vma->vm_end - vma->vm_start; @@ -1983,10 +2006,12 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma) atomic_long_add(user_extra, &user->locked_vm); vma->vm_mm->locked_vm += extra; counter->data->nr_locked = extra; + if (vma->vm_flags & VM_WRITE) + counter->data->writable = 1; + unlock: mutex_unlock(&counter->mmap_mutex); - vma->vm_flags &= ~VM_MAYWRITE; vma->vm_flags |= VM_RESERVED; vma->vm_ops = &perf_mmap_vmops; @@ -2163,11 +2188,38 @@ struct perf_output_handle { unsigned long head; unsigned long offset; int nmi; - int overflow; + int sample; int locked; unsigned long flags; }; +static bool perf_output_space(struct perf_mmap_data *data, + unsigned int offset, unsigned int head) +{ + unsigned long tail; + unsigned long mask; + + if (!data->writable) + return true; + + mask = (data->nr_pages << PAGE_SHIFT) - 1; + /* + * Userspace could choose to issue a mb() before updating the tail + * pointer. So that all reads will be completed before the write is + * issued. + */ + tail = ACCESS_ONCE(data->user_page->data_tail); + smp_rmb(); + + offset = (offset - tail) & mask; + head = (head - tail) & mask; + + if ((int)(head - offset) < 0) + return false; + + return true; +} + static void perf_output_wakeup(struct perf_output_handle *handle) { atomic_set(&handle->data->poll, POLL_IN); @@ -2258,12 +2310,57 @@ out: local_irq_restore(handle->flags); } +static void perf_output_copy(struct perf_output_handle *handle, + const void *buf, unsigned int len) +{ + unsigned int pages_mask; + unsigned int offset; + unsigned int size; + void **pages; + + offset = handle->offset; + pages_mask = handle->data->nr_pages - 1; + pages = handle->data->data_pages; + + do { + unsigned int page_offset; + int nr; + + nr = (offset >> PAGE_SHIFT) & pages_mask; + page_offset = offset & (PAGE_SIZE - 1); + size = min_t(unsigned int, PAGE_SIZE - page_offset, len); + + memcpy(pages[nr] + page_offset, buf, size); + + len -= size; + buf += size; + offset += size; + } while (len); + + handle->offset = offset; + + /* + * Check we didn't copy past our reservation window, taking the + * possible unsigned int wrap into account. + */ + WARN_ON_ONCE(((long)(handle->head - handle->offset)) < 0); +} + +#define perf_output_put(handle, x) \ + perf_output_copy((handle), &(x), sizeof(x)) + static int perf_output_begin(struct perf_output_handle *handle, struct perf_counter *counter, unsigned int size, - int nmi, int overflow) + int nmi, int sample) { struct perf_mmap_data *data; unsigned int offset, head; + int have_lost; + struct { + struct perf_event_header header; + u64 id; + u64 lost; + } lost_event; /* * For inherited counters we send all the output towards the parent. @@ -2276,19 +2373,25 @@ static int perf_output_begin(struct perf_output_handle *handle, if (!data) goto out; - handle->data = data; - handle->counter = counter; - handle->nmi = nmi; - handle->overflow = overflow; + handle->data = data; + handle->counter = counter; + handle->nmi = nmi; + handle->sample = sample; if (!data->nr_pages) goto fail; + have_lost = atomic_read(&data->lost); + if (have_lost) + size += sizeof(lost_event); + perf_output_lock(handle); do { offset = head = atomic_long_read(&data->head); head += size; + if (unlikely(!perf_output_space(data, offset, head))) + goto fail; } while (atomic_long_cmpxchg(&data->head, offset, head) != offset); handle->offset = offset; @@ -2297,55 +2400,27 @@ static int perf_output_begin(struct perf_output_handle *handle, if ((offset >> PAGE_SHIFT) != (head >> PAGE_SHIFT)) atomic_set(&data->wakeup, 1); + if (have_lost) { + lost_event.header.type = PERF_EVENT_LOST; + lost_event.header.misc = 0; + lost_event.header.size = sizeof(lost_event); + lost_event.id = counter->id; + lost_event.lost = atomic_xchg(&data->lost, 0); + + perf_output_put(handle, lost_event); + } + return 0; fail: - perf_output_wakeup(handle); + atomic_inc(&data->lost); + perf_output_unlock(handle); out: rcu_read_unlock(); return -ENOSPC; } -static void perf_output_copy(struct perf_output_handle *handle, - const void *buf, unsigned int len) -{ - unsigned int pages_mask; - unsigned int offset; - unsigned int size; - void **pages; - - offset = handle->offset; - pages_mask = handle->data->nr_pages - 1; - pages = handle->data->data_pages; - - do { - unsigned int page_offset; - int nr; - - nr = (offset >> PAGE_SHIFT) & pages_mask; - page_offset = offset & (PAGE_SIZE - 1); - size = min_t(unsigned int, PAGE_SIZE - page_offset, len); - - memcpy(pages[nr] + page_offset, buf, size); - - len -= size; - buf += size; - offset += size; - } while (len); - - handle->offset = offset; - - /* - * Check we didn't copy past our reservation window, taking the - * possible unsigned int wrap into account. - */ - WARN_ON_ONCE(((long)(handle->head - handle->offset)) < 0); -} - -#define perf_output_put(handle, x) \ - perf_output_copy((handle), &(x), sizeof(x)) - static void perf_output_end(struct perf_output_handle *handle) { struct perf_counter *counter = handle->counter; @@ -2353,7 +2428,7 @@ static void perf_output_end(struct perf_output_handle *handle) int wakeup_events = counter->attr.wakeup_events; - if (handle->overflow && wakeup_events) { + if (handle->sample && wakeup_events) { int events = atomic_inc_return(&data->events); if (events >= wakeup_events) { atomic_sub(wakeup_events, &data->events); @@ -2958,7 +3033,7 @@ static void perf_log_throttle(struct perf_counter *counter, int enable) } /* - * Generic counter overflow handling. + * Generic counter overflow handling, sampling. */ int perf_counter_overflow(struct perf_counter *counter, int nmi, |