Re: [Xenomai-help] Adeos/Xenomai Arm Port

["Schlägl Manfred jun." <manfred.schlaegl@domain.hid>]

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On Tue, 2006-10-17 at 17:39 +0200, Schlägl Manfred jun. wrote:

> 5. latency
> 
> For periodic user-mode task i need very high periods > 1000us.
> 
> 
> Here are the latency-checks with printk's of the ioctls:
> 
> -sh-3.00# ./run -- -t 1
> *
> *
> * Type ^C to stop this application.
> *
> *
> == Sampling period: 100 us
> == Test mode: in-kernel periodic task
> == All results in microseconds
> [42949519.180000] rt_tmbench_ioctl_rt: request 1076364816 -> ret =
> -ENOTTY(-25)
> latency: failed to start in-kernel timer benchmark, code -25
> [42949523.000000] rt_tmbench_ioctl_nrt: request -1071118831 -> ret =
> -ENOTTY(-25)
> ---|------------|------------|------------|--------|-------------------------
> RTS|-1096532.504|       0.001|      93.252|   93340|
> 00:00:03/00:00:03
> 
> -sh-3.00# ./run -- -t 2
> *
> *
> * Type ^C to stop this application.
> *
> *
> == Sampling period: 100 us
> == Test mode: in-kernel timer handler
> == All results in microseconds
> [42949529.090000] rt_tmbench_ioctl_rt: request 1076364816 -> ret =
> -ENOTTY(-25)
> latency: failed to start in-kernel timer benchmark, code -25
> [42949534.680000] rt_tmbench_ioctl_nrt: request -1071118831 -> ret =
> -ENOTTY(-25)
> ---|------------|------------|------------|--------|-------------------------
> RTS|-1093751.320|       0.001|      93.252|   93340|
> 00:00:04/00:00:04
> 
> 
> Userspace-codes differ from kernelspace-codes, I think...



Yes it does!!!



#define RTTST_RTIOC_TMBENCH_START \
    _IOW(RTIOC_TYPE_TESTING, 0x10, struct rttst_tmbench_config) 

two different results in kernel-/user-space

sizeof(struct rttst_tmbench_config) 
-> kernel 	32
-> user		40


typedef struct rttst_tmbench_config {
    int                     mode;
    uint64_t                period;
    int                     priority;
    int                     warmup_loops;
    int                     histogram_size;
    int                     histogram_bucketsize;
    int                     freeze_max;
} rttst_tmbench_config_t;

sizeof(struct rttst_tmbench_config_t)
-> kernel	32	(uses packed-structure)
-> user		40	(uses unpacked-structure)

sizeof(uint64_t)
-> kernel	8
-> user		8

sizeof(int)
-> kernel	4
-> user		4


Difference has something to do with the internal structure of
rttst_tmbench_config.


Solution 1: Force userspace-app and kernel to use packed structure
--------------
typedef struct rttst_tmbench_config {
    int                     mode;
    uint64_t                period;
    int                     priority;
    int                     warmup_loops;
    int                     histogram_size;
    int                     histogram_bucketsize;
    int                     freeze_max;
} __attribute__((packed)) rttst_tmbench_config_t;

sizeof(struct rttst_tmbench_config_t)
-> kernel	32	(uses packed-structure)
-> user		32	(uses packed-structure)

Has to be done to all structures! (compiler-flag -fpack-struct)

Problems: 
 * problems with libs (see
http://gcc.gnu.org/ml/gcc-help/2005-01/msg00257.html)
 * possibly problems with typedef ????


Solution 2: Force userspace-app and kernel to use unpacked structure
--------------
typedef struct rttst_tmbench_config {
    int                     mode;
    uint64_t                period;
    int                     priority;
    int                     warmup_loops;
    int                     histogram_size;
    int                     histogram_bucketsize;
    int                     freeze_max;
} __attribute__((unpacked)) rttst_tmbench_config_t;


Kernel ignores the attribute!

Theoretically:
sizeof(struct rttst_tmbench_config_t)
-> kernel	40	(uses unpacked-structure)
-> user		40	(uses unpacked-structure)

Has to be done to all structures! 




Solution 3:
--------------
change kernel-configuration to use unpacked structures by default.



	- Manfred Schlaegl


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