Look, until you have any numbers in hands it's impossible to say
which one is faster.
Please measure N d_alloc()'s on i686 and some other archs w/o string operations
and compare whether your patch improves something or not.
Kirill
rae l wrote:
> On 7/13/07, Kirill Korotaev <[email protected]> wrote:
>
>>This doesn't look worth zeroing half of the struct
>>when it is initialized to non-zeros then.
>
> But why?
>
> My reason to think it's better and faster is that:
> 1. the code will be shorter if it calls zalloc and then removes the
> NULL and zero initilization;
> 2. in the assembly code objdumped, many mov operations reduced, such as:
> movl $0,0x40(%ebp)
> ...
> this style of zero initialization occupies 7 bytes per line
> (i386), and then multiply 7 lines,
>
> 3. the only change is that calls to kmem_cache_zalloc other than
> kmem_cache_alloc, it's just an extra memset is called, as we all know
> the memset implimentation is string operation, that's rather fast.
>
>
>>Denis Cheng wrote:
>>
>>>>From 4d87e14b67890f06885a76b5792ca034de2e9d06 Mon Sep 17 00:00:00 2001
>>>From: Denis Cheng <[email protected]>
>>>Date: Thu, 12 Jul 2007 11:53:58 +0800
>>>Subject: [PATCH] replace kmem_cache_alloc with kmem_cache_zalloc to
>>>remove some following zero initializations.
>>>
>>>Signed-off-by: Denis Cheng <[email protected]>
>>>---
>>> fs/dcache.c | 12 ++----------
>>> 1 files changed, 2 insertions(+), 10 deletions(-)
>>>
>>>diff --git a/fs/dcache.c b/fs/dcache.c
>>>index 0e73aa0..8c559b2 100644
>>>--- a/fs/dcache.c
>>>+++ b/fs/dcache.c
>>>@@ -898,7 +898,7 @@ struct dentry *d_alloc(struct dentry * parent, const
>>>struct qstr *name)
>>> struct dentry *dentry;
>>> char *dname;
>>>
>>>- dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
>>>+ dentry = kmem_cache_zalloc(dentry_cache, GFP_KERNEL);
>>> if (!dentry)
>>> return NULL;
>>>
>>>@@ -921,15 +921,7 @@ struct dentry *d_alloc(struct dentry * parent,
>>>const struct qstr *name)
>>> atomic_set(&dentry->d_count, 1);
>>> dentry->d_flags = DCACHE_UNHASHED;
>>> spin_lock_init(&dentry->d_lock);
>>>- dentry->d_inode = NULL;
>>>- dentry->d_parent = NULL;
>>>- dentry->d_sb = NULL;
>>>- dentry->d_op = NULL;
>>>- dentry->d_fsdata = NULL;
>>>- dentry->d_mounted = 0;
>>>-#ifdef CONFIG_PROFILING
>>>- dentry->d_cookie = NULL;
>>>-#endif
>>>+
>>> INIT_HLIST_NODE(&dentry->d_hash);
>>> INIT_LIST_HEAD(&dentry->d_lru);
>>> INIT_LIST_HEAD(&dentry->d_subdirs);
>>
>>
>
>
-
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