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Date: Thu, 11 Apr 2013 10:59:22 -0700 From: Casey Schaufler <casey@...aufler-ca.com> To: Tomasz Stanislawski <t.stanislaws@...sung.com> CC: linux-security-module@...r.kernel.org, m.szyprowski@...sung.com, kyungmin.park@...sung.com, r.krypa@...sung.com, linux-kernel@...r.kernel.org, Casey Schaufler <casey@...aufler-ca.com> Subject: Re: [RFC] security: smack: add hash table for smack for quick label searching On 4/11/2013 1:46 AM, Tomasz Stanislawski wrote: > Hi everyone, > I am a developer working on optimization of the TIZEN system. > Recently, I've discovered a performance issue in SMACK subsystem. > I used the PERF tool to find performance bottlenecks. > > The test scenario was simple. Run multiple applications and > see what the system does using the following command: > > perf record -a -g > > Next, see the results with the command: > > perf report -s symbol -g graph,0.5 > > Among the many lines, the following ones are especially interesting: > > 5.96% [k] smk_find_entry > | > |--5.06%-- smk_access > | | > | --4.99%-- smk_curacc > | | > | |--3.79%-- smack_ptrace_access_check > | | security_ptrace_access_check > | | __ptrace_may_access > | | ptrace_may_access > | | | > | | --3.78%-- mm_access > | | mm_for_maps > | | m_start > | | seq_read > | | vfs_read > | | sys_read > | | ret_fast_syscall > | | | > | | --3.19%-- (nil) > | | > | --0.71%-- smack_inode_permission > | security_inode_permission > | inode_permission > | > --0.89%-- smack_to_secid > smack_socket_getpeersec_dgram > security_socket_getpeersec_dgram > | > --0.54%-- unix_stream_sendmsg > > 4.63% [k] strcmp > | > |--2.16%-- smk_find_entry > | | > | --1.92%-- smk_access > | | > | --1.85%-- smk_curacc > | | > | --1.20%-- smack_ptrace_access_check > | security_ptrace_access_check > | __ptrace_may_access > | ptrace_may_access > | mm_access > | mm_for_maps > | m_start > | seq_read > | vfs_read > | sys_read > | ret_fast_syscall > | | > | --0.99%-- (nil) > | > --2.14%-- smk_access > | > --2.11%-- smk_curacc > | > --1.75%-- smack_ptrace_access_check > security_ptrace_access_check > __ptrace_may_access > ptrace_may_access > | > --1.73%-- mm_access > mm_for_maps > m_start > seq_read > vfs_read > sys_read > ret_fast_syscall > | > --1.40%-- (nil) > > To sum up, the result indicates that the CPU spents circa 8% (2.16% + 5.96%) > of cycles searching for a SMACK label in the smk_find_entry function. > The function iterates through smack_known_list to find an entry. > The further analysis showed that the size of the list can reach even 600. > I measured that it takes circa 200 tries to find an entry on average. > The value was computed as a total number iterations in the smk_find_entry's > loop divided by the times smk_find_entry was called in a time-window of > the length of 10 seconds. > > IMO, this is a serious performance issue which scales badly with > a complexity of the system. > > I implemented a patch that makes a use of a hash table to quicken searching > for SMACK's labels. The patch is rebased onto the latest v3.9-rc6 kernel. > The code is thread-safe (I hope) because it shares the RCU mechanism > and locks with smack_known_list. > > There is still some place for improvements like: > a) using struct hlist_head instead of struct list_head to reduce > the memory size of the hash table. > > OR > > b) use smack_known::list instead of introducing smack_known::htab_list > and modify all smack_known_list related code to iterate over > the hash table. > > I decided to postpone the mentioned improvements for a sake of simplicity > of this RFC. After applying the patch, the smk_find_entry overhead was > reduced to mere 0.05% of CPU cycles. > > I hope you find the measurement and the patch useful. > All comments are welcome. NAK There will be no hash tables in Smack. The correct solution is simple. In the task_smack structure there are two Smack label pointers, smk_task and smk_forked. Replace these fields with pointers to the smack_known structures that contain the Smack label pointers used today. This will require trivial changes throughout the Smack code to accommodate the type change and a few logical twists around smk_import. It will eliminate the need for smk_lookup_entry. > > Regards, > Tomasz Stanislawski > > > Tomasz Stanislawski (1): > security: smack: add hash table for smack for quick label searching > > security/smack/smack.h | 5 +++++ > security/smack/smack_access.c | 33 +++++++++++++++++++++++++++++++-- > security/smack/smack_lsm.c | 21 +++++++++++++++------ > 3 files changed, 51 insertions(+), 8 deletions(-) > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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