| Message ID | alpine.DEB.1.10.0810271918390.19731@gandalf.stny.rr.com |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
On Mon, 27 Oct 2008 19:32:11 -0400 (EDT)
Steven Rostedt <rostedt@goodmis.org> wrote:
> Attached is a patch that I used for counting.
If we could get something like that into mainline then I can
stop maintaining profile-likely-unlikely-macros.patch, which would
be welcome.
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On Mon, Oct 27, 2008 at 07:32:11PM -0400, Steven Rostedt wrote: > Attached is a patch that I used for counting. > > Here's my results: > # cat /debug/tracing/ftrace_null > 45 > # cat /debug/tracing/ftrace_nonnull > 7 > > Ah, seems that there is cases where it is nonnull more often. Anyway, it > obviously is not a fast path (total of 52). Even if it was all null, it is > not big enough to call for the confusion. Silly question --- what was your test workload? - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Oct 27, 2008 at 7:32 PM, Steven Rostedt <rostedt@goodmis.org> wrote: > > On Mon, 27 Oct 2008, Mike Snitzer wrote: > >> Please see: e6022603b9aa7d61d20b392e69edcdbbc1789969 >> >> Having a look at the LKML archives this was raised back in 2006: >> http://lkml.org/lkml/2006/6/23/337 >> >> I'm not interested in whether unlikely() actually helps here. >> >> I'm still missing _why_ rsv is mostly NULL at this callsite, as Andrew >> asserted here: >> http://lkml.org/lkml/2006/6/23/400 >> >> And then Steve here: http://lkml.org/lkml/2006/6/24/76 >> Where he said: >> "The problem is that in these cases the pointer is NULL several thousands >> of times for every time it is not NULL (if ever). The non-NULL case is >> where an error occurred or something very special. So I don't see how >> the if here is a problem?" >> >> I'm missing which error or what "something very special" is the >> unlikely() reason for having rsv be NULL. >> >> Looking at the code; ext3_clear_inode() is _the_ place where the >> i_block_alloc_info is cleaned up. In my testing the rsv is _never_ >> NULL if the file was open for writing. Are we saying that reads are >> much more common than writes? May be a reasonable assumption but >> saying as much is very different than what Steve seemed to be eluding >> to... >> >> Anyway, I'd appreciate some clarification here. > > Attached is a patch that I used for counting. > > Here's my results: > # cat /debug/tracing/ftrace_null > 45 > # cat /debug/tracing/ftrace_nonnull > 7 > > Ah, seems that there is cases where it is nonnull more often. Anyway, it > obviously is not a fast path (total of 52). Even if it was all null, it is > not big enough to call for the confusion. What was your workload that resulted in this break-down? AFAIK you'd have 100% in ftrace_nonnull if you simply opened new files and wrote to them. > I'd suggest removing the if conditional, and just calling kfree. Yes, probably. thanks, Mike -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, 27 Oct 2008, Theodore Tso wrote: > On Mon, Oct 27, 2008 at 07:32:11PM -0400, Steven Rostedt wrote: > > Attached is a patch that I used for counting. > > > > Here's my results: > > # cat /debug/tracing/ftrace_null > > 45 > > # cat /debug/tracing/ftrace_nonnull > > 7 > > > > Ah, seems that there is cases where it is nonnull more often. Anyway, it > > obviously is not a fast path (total of 52). Even if it was all null, it is > > not big enough to call for the confusion. > > Silly question --- what was your test workload? Hehe, I just booted the box. The counting started right away, so I just looked at the work load. Anyway, I'm writing a generic "unlikely" profiler that should make Andrew happy. And this will also catch this case as well. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
--- fs/ext3/super.c | 8 ++++ kernel/trace/Makefile | 1 kernel/trace/trace_null.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 84 insertions(+), 1 deletion(-) Index: linux-tip.git/fs/ext3/super.c =================================================================== --- linux-tip.git.orig/fs/ext3/super.c 2008-10-24 10:08:43.000000000 -0400 +++ linux-tip.git/fs/ext3/super.c 2008-10-27 19:01:22.000000000 -0400 @@ -502,6 +502,9 @@ static void destroy_inodecache(void) kmem_cache_destroy(ext3_inode_cachep); } +extern void ftrace_null(void); +extern void ftrace_nonnull(void); + static void ext3_clear_inode(struct inode *inode) { struct ext3_block_alloc_info *rsv = EXT3_I(inode)->i_block_alloc_info; @@ -519,8 +522,11 @@ static void ext3_clear_inode(struct inod #endif ext3_discard_reservation(inode); EXT3_I(inode)->i_block_alloc_info = NULL; - if (unlikely(rsv)) + if (unlikely(rsv)) { + ftrace_nonnull(); kfree(rsv); + } else + ftrace_null(); } static inline void ext3_show_quota_options(struct seq_file *seq, struct super_block *sb) Index: linux-tip.git/kernel/trace/Makefile =================================================================== --- linux-tip.git.orig/kernel/trace/Makefile 2008-10-27 19:00:03.000000000 -0400 +++ linux-tip.git/kernel/trace/Makefile 2008-10-27 19:08:25.000000000 -0400 @@ -13,6 +13,7 @@ endif obj-$(CONFIG_FUNCTION_TRACER) += libftrace.o obj-$(CONFIG_RING_BUFFER) += ring_buffer.o +obj-$(CONFIG_TRACING) += trace_null.o obj-$(CONFIG_TRACING) += trace.o obj-$(CONFIG_CONTEXT_SWITCH_TRACER) += trace_sched_switch.o obj-$(CONFIG_SYSPROF_TRACER) += trace_sysprof.o Index: linux-tip.git/kernel/trace/trace_null.c =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ linux-tip.git/kernel/trace/trace_null.c 2008-10-27 19:23:15.000000000 -0400 @@ -0,0 +1,76 @@ +/* + * Function profiler + * + * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com> + */ +#include <linux/kallsyms.h> +#include <linux/seq_file.h> +#include <linux/spinlock.h> +#include <linux/debugfs.h> +#include <linux/uaccess.h> +#include <linux/module.h> +#include <linux/ftrace.h> +#include <linux/hash.h> +#include <linux/fs.h> +#include <asm/local.h> +#include "trace.h" + + +static atomic_t ftrace_null_count; +static atomic_t ftrace_nonnull_count; + +void ftrace_null(void) +{ + atomic_inc(&ftrace_null_count); +} +EXPORT_SYMBOL(ftrace_null); + +void ftrace_nonnull(void) +{ + atomic_inc(&ftrace_nonnull_count); +} +EXPORT_SYMBOL(ftrace_nonnull); + +static ssize_t +tracing_read_long(struct file *filp, char __user *ubuf, + size_t cnt, loff_t *ppos) +{ + atomic_t *p = filp->private_data; + char buf[64]; + int r; + + r = sprintf(buf, "%d\n", atomic_read(p)); + + return simple_read_from_buffer(ubuf, cnt, ppos, buf, r); +} + +static struct file_operations tracing_read_long_fops = { + .open = tracing_open_generic, + .read = tracing_read_long, +}; + + +static __init int ftrace_null_init(void) +{ + struct dentry *d_tracer; + struct dentry *entry; + + d_tracer = tracing_init_dentry(); + + entry = debugfs_create_file("ftrace_null", 0444, d_tracer, + &ftrace_null_count, + &tracing_read_long_fops); + if (!entry) + pr_warning("Could not create debugfs 'ftrace_null' entry\n"); + + entry = debugfs_create_file("ftrace_nonnull", 0444, d_tracer, + &ftrace_nonnull_count, + &tracing_read_long_fops); + if (!entry) + pr_warning("Could not create debugfs 'ftrace_nonnull' entry\n"); + + + return 0; +} + +device_initcall(ftrace_null_init);