svn commit: r355227 - head/sys/fs/tmpfs

[Mateusz Guzik]

On 12/1/19, Konstantin Belousov <kostikbel at gmail.com> wrote:
> On Sat, Nov 30, 2019 at 04:41:48PM +0000, Mateusz Guzik wrote:
>> Author: mjg
>> Date: Sat Nov 30 16:41:47 2019
>> New Revision: 355227
>> URL: https://svnweb.freebsd.org/changeset/base/355227
>>
>> Log:
>>   tmpfs: add fast path to tmpfs_access for common case lookup
>>
>>   VEXEC consists of vast majority of all calls and almost all targets
>> have
>>   at least 0111.
> On what load VEXEC is the dominant access check ?
>

Note this is called for every directory to be traversed dooring lookup,
so for instance looking up "foo/bar/baz" performs 2 VEXEC checks.

Sample result from buildkernel. 64 is VEXEC.

dtrace -n 'fbt::tmpfs_access:entry { @[args[0]->a_accmode, ((struct
tmpfs_node *)args[0]->a_vp->v_data)->tn_mode & 0111] = count(); }'
dtrace: description 'fbt::tmpfs_access:entry ' matched 1 probe


      384       73                1
    16512        0                2
      128        0               68
      384        0              877
     4096        0             1049
      320       73             5965
     4096       73            32471
      128       73           145115
      256       73           160569
      256        0           999827
       64       73         32320731

>>
>> Modified:
>>   head/sys/fs/tmpfs/tmpfs_vnops.c
>>
>> Modified: head/sys/fs/tmpfs/tmpfs_vnops.c
>> ==============================================================================
>> --- head/sys/fs/tmpfs/tmpfs_vnops.c	Sat Nov 30 16:40:16 2019	(r355226)
>> +++ head/sys/fs/tmpfs/tmpfs_vnops.c	Sat Nov 30 16:41:47 2019	(r355227)
>> @@ -331,6 +331,12 @@ tmpfs_access(struct vop_access_args *v)
>>
>>  	node = VP_TO_TMPFS_NODE(vp);
>>
>> +	/*
>> +	 * Common case path lookup.
>> +	 */
>> +	if (__predict_true(accmode == VEXEC && (node->tn_mode & 0111) == 0111))
> The 0111 must be spelled as (S_IXUSR | S_IXGRP | S_IXOTH).
>

Ok.

>> +		return (0);
>> +
>>  	switch (vp->v_type) {
>>  	case VDIR:
>>  		/* FALLTHROUGH */
>


-- 
Mateusz Guzik <mjguzik gmail.com>