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authorWaiman Long <Waiman.Long@hp.com>2013-07-23 17:38:41 -0400
committerEric Paris <eparis@redhat.com>2013-07-25 13:02:18 -0400
commitfee7114298cf54bbd221cdb2ab49738be8b94f4c (patch)
treed89946b8a81e44f56fa7c8c41aaedf128d112e95 /security/selinux/ss/ebitmap.c
parentselinux: remove the BUG_ON() from selinux_skb_xfrm_sid() (diff)
downloadlinux-dev-fee7114298cf54bbd221cdb2ab49738be8b94f4c.tar.xz
linux-dev-fee7114298cf54bbd221cdb2ab49738be8b94f4c.zip
SELinux: Reduce overhead of mls_level_isvalid() function call
While running the high_systime workload of the AIM7 benchmark on a 2-socket 12-core Westmere x86-64 machine running 3.10-rc4 kernel (with HT on), it was found that a pretty sizable amount of time was spent in the SELinux code. Below was the perf trace of the "perf record -a -s" of a test run at 1500 users: 5.04% ls [kernel.kallsyms] [k] ebitmap_get_bit 1.96% ls [kernel.kallsyms] [k] mls_level_isvalid 1.95% ls [kernel.kallsyms] [k] find_next_bit The ebitmap_get_bit() was the hottest function in the perf-report output. Both the ebitmap_get_bit() and find_next_bit() functions were, in fact, called by mls_level_isvalid(). As a result, the mls_level_isvalid() call consumed 8.95% of the total CPU time of all the 24 virtual CPUs which is quite a lot. The majority of the mls_level_isvalid() function invocations come from the socket creation system call. Looking at the mls_level_isvalid() function, it is checking to see if all the bits set in one of the ebitmap structure are also set in another one as well as the highest set bit is no bigger than the one specified by the given policydb data structure. It is doing it in a bit-by-bit manner. So if the ebitmap structure has many bits set, the iteration loop will be done many times. The current code can be rewritten to use a similar algorithm as the ebitmap_contains() function with an additional check for the highest set bit. The ebitmap_contains() function was extended to cover an optional additional check for the highest set bit, and the mls_level_isvalid() function was modified to call ebitmap_contains(). With that change, the perf trace showed that the used CPU time drop down to just 0.08% (ebitmap_contains + mls_level_isvalid) of the total which is about 100X less than before. 0.07% ls [kernel.kallsyms] [k] ebitmap_contains 0.05% ls [kernel.kallsyms] [k] ebitmap_get_bit 0.01% ls [kernel.kallsyms] [k] mls_level_isvalid 0.01% ls [kernel.kallsyms] [k] find_next_bit The remaining ebitmap_get_bit() and find_next_bit() functions calls are made by other kernel routines as the new mls_level_isvalid() function will not call them anymore. This patch also improves the high_systime AIM7 benchmark result, though the improvement is not as impressive as is suggested by the reduction in CPU time spent in the ebitmap functions. The table below shows the performance change on the 2-socket x86-64 system (with HT on) mentioned above. +--------------+---------------+----------------+-----------------+ | Workload | mean % change | mean % change | mean % change | | | 10-100 users | 200-1000 users | 1100-2000 users | +--------------+---------------+----------------+-----------------+ | high_systime | +0.1% | +0.9% | +2.6% | +--------------+---------------+----------------+-----------------+ Signed-off-by: Waiman Long <Waiman.Long@hp.com> Acked-by: Stephen Smalley <sds@tycho.nsa.gov> Signed-off-by: Paul Moore <pmoore@redhat.com> Signed-off-by: Eric Paris <eparis@redhat.com>
Diffstat (limited to 'security/selinux/ss/ebitmap.c')
-rw-r--r--security/selinux/ss/ebitmap.c20
1 files changed, 18 insertions, 2 deletions
diff --git a/security/selinux/ss/ebitmap.c b/security/selinux/ss/ebitmap.c
index 30f119b1d1ec..820313a04d49 100644
--- a/security/selinux/ss/ebitmap.c
+++ b/security/selinux/ss/ebitmap.c
@@ -213,7 +213,12 @@ netlbl_import_failure:
}
#endif /* CONFIG_NETLABEL */
-int ebitmap_contains(struct ebitmap *e1, struct ebitmap *e2)
+/*
+ * Check to see if all the bits set in e2 are also set in e1. Optionally,
+ * if last_e2bit is non-zero, the highest set bit in e2 cannot exceed
+ * last_e2bit.
+ */
+int ebitmap_contains(struct ebitmap *e1, struct ebitmap *e2, u32 last_e2bit)
{
struct ebitmap_node *n1, *n2;
int i;
@@ -223,14 +228,25 @@ int ebitmap_contains(struct ebitmap *e1, struct ebitmap *e2)
n1 = e1->node;
n2 = e2->node;
+
while (n1 && n2 && (n1->startbit <= n2->startbit)) {
if (n1->startbit < n2->startbit) {
n1 = n1->next;
continue;
}
- for (i = 0; i < EBITMAP_UNIT_NUMS; i++) {
+ for (i = EBITMAP_UNIT_NUMS - 1; (i >= 0) && !n2->maps[i]; )
+ i--; /* Skip trailing NULL map entries */
+ if (last_e2bit && (i >= 0)) {
+ u32 lastsetbit = n2->startbit + i * EBITMAP_UNIT_SIZE +
+ __fls(n2->maps[i]);
+ if (lastsetbit > last_e2bit)
+ return 0;
+ }
+
+ while (i >= 0) {
if ((n1->maps[i] & n2->maps[i]) != n2->maps[i])
return 0;
+ i--;
}
n1 = n1->next;