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This patch uses the rcu_assign_pointer() API to eliminate a number of explicit
memory barriers from the SysV IPC code that uses RCU. It also restructures
the ipc_ids structure so that the array size is stored in the same memory
block as the array itself (see the new struct ipc_id_ary). This prevents the
race that the earlier code was subject to, where a reader could see a mismatch
between the size and the actual array. With the size stored with the array,
the possibility of mismatch is eliminated -- with out the need for careful
ordering and explicit memory barriers. This has been tested successfully on
i386 and ppc64.
Signed-off-by: <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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The lifetime of the ipc objects (sem array, msg queue, shm mapping) is
controlled by kern_ipc_perms->lock - a spinlock. There is no simple way to
reacquire this spinlock after it was dropped to
schedule()/kmalloc/copy_{to,from}_user/whatever.
The attached patch adds a reference count as a preparation to get rid of
sem_revalidate().
Signed-Off-By: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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From: Manfred Spraul <manfred@colorfullife.com>
cleanup of sysv ipc as a preparation for posix message queues:
- replace !CONFIG_SYSVIPC wrappers for copy_semundo and exit_sem with
static inline wrappers. Now the whole ipc/util.c file is only used if
CONFIG_SYSVIPC is set, use makefile magic instead of #ifdef.
- remove the prototypes for copy_semundo and exit_sem from kernel/fork.c
- they belong into a header file.
- create a new msgutil.c with the helper functions for message queues.
- cleanup the helper functions: run Lindent, add __user tags.
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PA-RISC also uses the 64-bit version of the IPC structs.
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AMD64 like IA64 needs to force IPC_64 in the IPC functions. This makes
2.5 compatible with 2.4 again.
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Uninlines some large functions in the ipc code.
Before:
text data bss dec hex filename
30226 224 192 30642 77b2 ipc/built-in.o
After:
text data bss dec hex filename
20274 224 192 20690 50d2 ipc/built-in.o
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Patch from Mingming, Rusty, Hugh, Dipankar, me:
- It greatly reduces the lock contention by having one lock per id.
The global spinlock is removed and a spinlock is added in
kern_ipc_perm structure.
- Uses ReadCopyUpdate in grow_ary() for locking-free resizing.
- In the places where ipc_rmid() is called, delay calling ipc_free()
to RCU callbacks. This is to prevent ipc_lock() returning an invalid
pointer after ipc_rmid(). In addition, use the workqueue to enable
RCU freeing vmalloced entries.
Also some other changes:
- Remove redundant ipc_lockall/ipc_unlockall
- Now ipc_unlock() directly takes IPC ID pointer as argument, avoid
extra looking up the array.
The changes are made based on the input from Huge Dickens, Manfred
Spraul and Dipankar Sarma. In addition, Cliff White has run OSDL's
dbt1 test on a 2 way against the earlier version of this patch.
Results shows about 2-6% improvement on the average number of
transactions per second. Here is the summary of his tests:
2.5.42-mm2 2.5.42-mm2-ipclock
-----------------------------
Average over 5 runs 85.0 BT 89.8 BT
Std Deviation 5 runs 7.4 BT 1.0 BT
Average over 4 best 88.15 BT 90.2 BT
Std Deviation 4 best 2.8 BT 0.5 BT
Also, another test today from Bill Hartner:
I tested Mingming's RCU ipc lock patch using a *new* microbenchmark - semopbench.
semopbench was written to test the performance of Mingming's patch.
I also ran a 3 hour stress and it completed successfully.
Explanation of the microbenchmark is below the results.
Here is a link to the microbenchmark source.
http://www-124.ibm.com/developerworks/opensource/linuxperf/semopbench/semopbench.c
SUT : 8-way 700 Mhz PIII
I tested 2.5.44-mm2 and 2.5.44-mm2 + RCU ipc patch
>semopbench -g 64 -s 16 -n 16384 -r > sem.results.out
>readprofile -m /boot/System.map | sort -n +0 -r > sem.profile.out
The metric is seconds / per repetition. Lower is better.
kernel run 1 run 2
seconds seconds
================== ======= =======
2.5.44-mm2 515.1 515.4
2.5.44-mm2+rcu-ipc 46.7 46.7
With Mingming's patch, the test completes 10X faster.
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- sync up more with Alan
- Urban Widmark: smbfs and HIGHMEM fix
- Chris Mason: reiserfs tail unpacking fix ("null bytes in reiserfs files")
- Adan Richter: new cpia usb ID
- Hugh Dickins: misc small sysv ipc fixes
- Andries Brouwer: remove overly restrictive sector size check for
SCSI cd-roms
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