A debugfs file named `readahead/events' is created according to advises from J?rn Engel, Andrew Morton and Ingo Oeser. It reveals various read-ahead activities/events, and is vital to the testing. If you are experiencing performance problems, or want to help improve the read-ahead logic, please send me the debug data. Thanks. - Preparations ## First compile kernel with CONFIG_DEBUG_READAHEAD mkdir /debug mount -t debug none /debug - For each session with distinct access pattern echo > /debug/readahead/events # reset the counters # echo > /var/log/kern.log # you may want to backup it first # echo 3 > /debug/readahead/debug_level # show verbose printk traces ## do one benchmark/task # echo 1 > /debug/readahead/debug_level # revert to normal value cp /debug/readahead/events readahead-events-`date +'%F_%R'` # bzip2 -c /var/log/kern.log > kern.log-`date +'%F_%R'`.bz2 The commented out commands can uncover more detailed file accesses, which are useful sometimes. Note that the log file can grow huge! Signed-off-by: Wu Fengguang Signed-off-by: Andrew Morton --- linux-2.6.19-rc4-mm1.orig/mm/readahead.c +++ linux-2.6.19-rc4-mm1/mm/readahead.c @@ -26,6 +26,66 @@ #define MAX_RA_PAGES (VM_MAX_READAHEAD*1024 / PAGE_CACHE_SIZE) #define MIN_RA_PAGES DIV_ROUND_UP(VM_MIN_READAHEAD*1024, PAGE_CACHE_SIZE) +/* + * Detailed classification of read-ahead behaviors. + */ +#define RA_CLASS_SHIFT 4 +#define RA_CLASS_MASK ((1 << RA_CLASS_SHIFT) - 1) +enum ra_class { + RA_CLASS_ALL, + RA_CLASS_INITIAL, + RA_CLASS_STATE, + RA_CLASS_CONTEXT, + RA_CLASS_CONTEXT_AGGRESSIVE, + RA_CLASS_BACKWARD, + RA_CLASS_THRASHING, + RA_CLASS_NONE, + RA_CLASS_COUNT +}; + +/* Read-ahead events to be accounted. */ +enum ra_event { + RA_EVENT_CACHE_MISS, /* read cache misses */ + RA_EVENT_RANDOM_READ, /* random reads */ + RA_EVENT_IO_CONGESTION, /* i/o congestion */ + RA_EVENT_IO_CACHE_HIT, /* canceled i/o due to cache hit */ + RA_EVENT_IO_BLOCK, /* wait for i/o completion */ + + RA_EVENT_READAHEAD, /* read-ahead issued */ + RA_EVENT_READAHEAD_HIT, /* read-ahead page hit */ + RA_EVENT_LOOKAHEAD, /* look-ahead issued */ + RA_EVENT_LOOKAHEAD_HIT, /* look-ahead mark hit */ + RA_EVENT_LOOKAHEAD_NOACTION, /* look-ahead mark ignored */ + RA_EVENT_READAHEAD_MMAP, /* read-ahead for mmap access */ + RA_EVENT_READAHEAD_EOF, /* read-ahead reaches EOF */ + RA_EVENT_READAHEAD_SHRINK, /* ra_size falls under previous la_size */ + RA_EVENT_READAHEAD_THRASHING, /* read-ahead thrashing happened */ + RA_EVENT_READAHEAD_MUTILATE, /* read-ahead mutilated by imbalanced aging */ + RA_EVENT_READAHEAD_RESCUE, /* read-ahead rescued */ + + RA_EVENT_READAHEAD_CUBE, + RA_EVENT_COUNT +}; + +#ifdef CONFIG_DEBUG_READAHEAD +u32 readahead_debug_level = 1; +static u32 disable_stateful_method; +static const char * const ra_class_name[]; +static void ra_account(struct file_ra_state *ra, enum ra_event e, int pages); +# define debug_inc(var) do { var++; } while (0) +# define debug_option(o) (o) +#else +# define ra_account(ra, e, pages) do { } while (0) +# define debug_inc(var) do { } while (0) +# define debug_option(o) (0) +# define readahead_debug_level (0) +#endif /* CONFIG_DEBUG_READAHEAD */ + +#define dprintk(args...) \ + do { if (readahead_debug_level >= 2) printk(KERN_DEBUG args); } while(0) +#define ddprintk(args...) \ + do { if (readahead_debug_level >= 3) printk(KERN_DEBUG args); } while(0) + void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page) { } @@ -395,6 +455,9 @@ int force_page_cache_readahead(struct ad offset += this_chunk; nr_to_read -= this_chunk; } + + ra_account(NULL, RA_EVENT_READAHEAD, ret); + return ret; } @@ -430,10 +493,16 @@ static inline int check_ra_success(struc int do_page_cache_readahead(struct address_space *mapping, struct file *filp, pgoff_t offset, unsigned long nr_to_read) { + unsigned long ret; + if (bdi_read_congested(mapping->backing_dev_info)) return -1; - return __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0); + ret = __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0); + + ra_account(NULL, RA_EVENT_READAHEAD, ret); + + return ret; } /* @@ -455,6 +524,10 @@ blockable_page_cache_readahead(struct ad actual = __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0); + ra_account(NULL, RA_EVENT_READAHEAD, actual); + dprintk("blockable-readahead(ino=%lu, ra=%lu+%lu) = %d\n", + mapping->host->i_ino, offset, nr_to_read, actual); + return check_ra_success(ra, nr_to_read, actual); } @@ -633,3 +706,208 @@ unsigned long max_sane_readahead(unsigne __get_zone_counts(&active, &inactive, &free, NODE_DATA(numa_node_id())); return min(nr, (inactive + free) / 2); } + +/* + * Read-ahead events accounting. + */ +#ifdef CONFIG_DEBUG_READAHEAD + +#include +#include +#include +#include + +static const char * const ra_class_name[] = { + "total", + "initial", + "state", + "context", + "contexta", + "backward", + "onthrash", + "none" +}; + +static const char * const ra_event_name[] = { + "cache_miss", + "random_read", + "io_congestion", + "io_cache_hit", + "io_block", + "readahead", + "readahead_hit", + "lookahead", + "lookahead_hit", + "lookahead_ignore", + "readahead_mmap", + "readahead_eof", + "readahead_shrink", + "readahead_thrash", + "readahead_mutilt", + "readahead_rescue" +}; + +static unsigned long ra_events[RA_CLASS_COUNT][RA_EVENT_COUNT][2]; + +static void ra_account(struct file_ra_state *ra, enum ra_event e, int pages) +{ + enum ra_class c; + + if (!readahead_debug_level) + return; + + if (e == RA_EVENT_READAHEAD_HIT && pages < 0) { + c = (ra->flags >> RA_CLASS_SHIFT) & RA_CLASS_MASK; + pages = -pages; + } else if (ra) + c = ra->flags & RA_CLASS_MASK; + else + c = RA_CLASS_NONE; + + if (!c) + c = RA_CLASS_NONE; + + ra_events[c][e][0] += 1; + ra_events[c][e][1] += pages; + + if (e == RA_EVENT_READAHEAD) + ra_events[c][RA_EVENT_READAHEAD_CUBE][1] += pages * pages; +} + +static int ra_events_show(struct seq_file *s, void *_) +{ + int i; + int c; + int e; + static const char event_fmt[] = "%-16s"; + static const char class_fmt[] = "%10s"; + static const char item_fmt[] = "%10lu"; + static const char percent_format[] = "%9lu%%"; + static const char * const table_name[] = { + "[table requests]", + "[table pages]", + "[table summary]"}; + + for (i = 0; i <= 1; i++) { + for (e = 0; e < RA_EVENT_COUNT; e++) { + ra_events[RA_CLASS_ALL][e][i] = 0; + for (c = RA_CLASS_INITIAL; c < RA_CLASS_NONE; c++) + ra_events[RA_CLASS_ALL][e][i] += ra_events[c][e][i]; + } + + seq_printf(s, event_fmt, table_name[i]); + for (c = 0; c < RA_CLASS_COUNT; c++) + seq_printf(s, class_fmt, ra_class_name[c]); + seq_puts(s, "\n"); + + for (e = 0; e < RA_EVENT_COUNT; e++) { + if (e == RA_EVENT_READAHEAD_CUBE) + continue; + if (e == RA_EVENT_READAHEAD_HIT && i == 0) + continue; + if (e == RA_EVENT_IO_BLOCK && i == 1) + continue; + + seq_printf(s, event_fmt, ra_event_name[e]); + for (c = 0; c < RA_CLASS_COUNT; c++) + seq_printf(s, item_fmt, ra_events[c][e][i]); + seq_puts(s, "\n"); + } + seq_puts(s, "\n"); + } + + seq_printf(s, event_fmt, table_name[2]); + for (c = 0; c < RA_CLASS_COUNT; c++) + seq_printf(s, class_fmt, ra_class_name[c]); + seq_puts(s, "\n"); + + seq_printf(s, event_fmt, "random_rate"); + for (c = 0; c < RA_CLASS_COUNT; c++) + seq_printf(s, percent_format, + (ra_events[c][RA_EVENT_RANDOM_READ][0] * 100) / + ((ra_events[c][RA_EVENT_RANDOM_READ][0] + + ra_events[c][RA_EVENT_READAHEAD][0]) | 1)); + seq_puts(s, "\n"); + + seq_printf(s, event_fmt, "ra_hit_rate"); + for (c = 0; c < RA_CLASS_COUNT; c++) + seq_printf(s, percent_format, + (ra_events[c][RA_EVENT_READAHEAD_HIT][1] * 100) / + (ra_events[c][RA_EVENT_READAHEAD][1] | 1)); + seq_puts(s, "\n"); + + seq_printf(s, event_fmt, "la_hit_rate"); + for (c = 0; c < RA_CLASS_COUNT; c++) + seq_printf(s, percent_format, + (ra_events[c][RA_EVENT_LOOKAHEAD_HIT][0] * 100) / + (ra_events[c][RA_EVENT_LOOKAHEAD][0] | 1)); + seq_puts(s, "\n"); + + seq_printf(s, event_fmt, "var_ra_size"); + for (c = 0; c < RA_CLASS_COUNT; c++) + seq_printf(s, item_fmt, + (ra_events[c][RA_EVENT_READAHEAD_CUBE][1] - + ra_events[c][RA_EVENT_READAHEAD][1] * + (ra_events[c][RA_EVENT_READAHEAD][1] / + (ra_events[c][RA_EVENT_READAHEAD][0] | 1))) / + (ra_events[c][RA_EVENT_READAHEAD][0] | 1)); + seq_puts(s, "\n"); + + seq_printf(s, event_fmt, "avg_ra_size"); + for (c = 0; c < RA_CLASS_COUNT; c++) + seq_printf(s, item_fmt, + (ra_events[c][RA_EVENT_READAHEAD][1] + + ra_events[c][RA_EVENT_READAHEAD][0] / 2) / + (ra_events[c][RA_EVENT_READAHEAD][0] | 1)); + seq_puts(s, "\n"); + + seq_printf(s, event_fmt, "avg_la_size"); + for (c = 0; c < RA_CLASS_COUNT; c++) + seq_printf(s, item_fmt, + (ra_events[c][RA_EVENT_LOOKAHEAD][1] + + ra_events[c][RA_EVENT_LOOKAHEAD][0] / 2) / + (ra_events[c][RA_EVENT_LOOKAHEAD][0] | 1)); + seq_puts(s, "\n"); + + return 0; +} + +static int ra_events_open(struct inode *inode, struct file *file) +{ + return single_open(file, ra_events_show, NULL); +} + +static ssize_t ra_events_write(struct file *file, const char __user *buf, + size_t size, loff_t *offset) +{ + memset(ra_events, 0, sizeof(ra_events)); + return 1; +} + +static struct file_operations ra_events_fops = { + .owner = THIS_MODULE, + .open = ra_events_open, + .write = ra_events_write, + .read = seq_read, + .llseek = seq_lseek, + .release = single_release, +}; + +static int __init readahead_init(void) +{ + struct dentry *root; + + root = debugfs_create_dir("readahead", NULL); + + debugfs_create_file("events", 0644, root, NULL, &ra_events_fops); + + debugfs_create_u32("debug_level", 0644, root, &readahead_debug_level); + debugfs_create_bool("disable_stateful_method", 0644, root, + &disable_stateful_method); + + return 0; +} + +module_init(readahead_init) + +#endif /* CONFIG_DEBUG_READAHEAD */ -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/