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SubjectRe: [RFC][PATCH 1/6] Storing ipcs into radix trees
Ingo Oeser wrote:
> Hi Nadia,
>
> good to see someone is pounding this old beast again :-)
>
> On Thursday 07 June 2007, Nadia.Derbey@bull.net wrote:
>
>>Index: linux-2.6.21/ipc/util.h
>>===================================================================
>>--- linux-2.6.21.orig/ipc/util.h 2007-06-07 11:00:30.000000000 +0200
>>+++ linux-2.6.21/ipc/util.h 2007-06-07 11:07:22.000000000 +0200
>>@@ -13,6 +13,8 @@
>> #define USHRT_MAX 0xffff
>> #define SEQ_MULTIPLIER (IPCMNI)
>>
>>+#define IPCS_MAX_SCAN_ENTRIES 256
>
>
> That ...
>
>
>>Index: linux-2.6.21/ipc/util.c
>>===================================================================
>>--- linux-2.6.21.orig/ipc/util.c 2007-06-07 11:00:30.000000000 +0200
>>+++ linux-2.6.21/ipc/util.c 2007-06-07 11:29:43.000000000 +0200
>>@@ -252,72 +241,94 @@ void __init ipc_init_proc_interface(cons
>> * @key: The key to find
>> *
>> * Requires ipc_ids.mutex locked.
>>- * Returns the identifier if found or -1 if not.
>>+ * Returns the LOCKED pointer to the ipc structure if found or NULL
>>+ * if not.
>>+ * If key is found ipc contains its ipc structure
>> */
>>
>>-int ipc_findkey(struct ipc_ids* ids, key_t key)
>>+struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key)
>> {
>>- int id;
>>- struct kern_ipc_perm* p;
>>- int max_id = ids->max_id;
>>+ struct kern_ipc_perm *ipc;
>>+ struct kern_ipc_perm *ipcs[IPCS_MAX_SCAN_ENTRIES];
>
>
> ... together with this means 4*256 -> 1k of precious stack space used.
> Please consider either lowering IPCS_MAX_SCAN_ENTRIES or kmalloc() that.
>
> Same problem with your third patch called
> "Changing the loops on a single ipcid into radix_tree_gang_lookup() calls"
>
> If you cannot sleep, try to lower that constant (e.g. 16-32).
> The current users use much smaller numbers.
>
> If you can sleep and performance goes down after lowering that constant,
> try to kmalloc these arrays (since kmalloc() of that small amount
> should succeed easily).
>
>
>
> Regards
>
> Ingo Oeser
>

Ingo,

You're completely right, but trying to lower the extraction size, I'm
afraid this will have an impact on performances.

Here are the results of a small test I did: I have run ctxbench on both
the 256 and and 16 entries versions

1) 256 entries:

[root@akt ctxbench-1.9]# echo 1000 > /proc/sys/kernel/msgmni
[root@akt ctxbench-1.9]# ./ctx -m -t300


Context switching benchmark v1.17
Using message queue for IPC control
Max iterations: 0 (zero = no limit)
Max runtime (sec): 300 (zero = no limit)
42523679 itterations in 300.005423 seconds = 141743/sec

2) 16 entries:

[root@akt ctxbench-1.9]# echo 1000 > /proc/sys/kernel/msgmni
[root@akt ctxbench-1.9]# ./ctx -m -t300


Context switching benchmark v1.17
Using message queue for IPC control
Max iterations: 0 (zero = no limit)
Max runtime (sec): 300 (zero = no limit)
41774255 itterations in 300.005334 seconds = 139245/sec

Will try with a dynamic allocation.

Regards,
Nadia


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