Re: Bug#561891: Bug 561891: Is FTBFS for fio on SuperH (sh4) resolved?

[Jens Axboe <axboe@kernel.dk>]

On 2011-08-25 10:33, Martin Steigerwald wrote:
> Hi!
> 
> I am putting upstream author Jens Axboe on CC.
> 
> Am Donnerstag, 25. August 2011 schrieb Nobuhiro Iwamatsu:
>> Hi,
> [...]
>>
>> 2011/8/3 Martin Steigerwald <ms@teamix.de>:
>>> Hello Nobuhiro, Paul, hello Debian SuperH maintainers, hello Jens,
>>>
>>> I am seeking information on the current status regarding
>>>
>>> Please support sh4
>>> http://bugs.debian.org/561891
>>>
>>> and eventually help in resolving it if it has not already been
>>> resolved.
>>>
>>> When I am reading
>>>
>>> http://buildd.debian-ports.org/status/package.php?p=fio&suite=unstabl
>>> e
>>>
>>> correctly, then fio 1.50-1 has been build 167d before on buildd
>>> kongou.
>>>
>>> So is this issue resolved?
>>>
>>> If not, please offer help. There is a partial patch mentioned earlier
>>> in the bug report.
>>
>> By this method, we cannot support both SH4 and SH4A. When we build
>> with machine of SH4A, a binary to work only in SH4A is built.
>> Because Debian SH team are supporting sh4 and sh4a in one binary, this
>> becomes the problem.
>> And this is a problem peculiar to Debian. It will not become the
>> problem in other distribution. (e.g., Gentoo)
>> It is necessary to check whether you do not do it whether we support
>> synco when we support both CPU's when we execute  *_barrier.
>> I think that this has a big overhead.
>>
>> I attached quick hack patch.
> 
> Jens, what do you think about such a patch? Please advice.
> 
> Nobuhiro, where do you think comes the big overhead from? In your patch 
> you check once at beginning for sinco capability. Do you refer to the if 
> statement you added in arch/arch-sh.h?
> 
> Ciao,

How about something like the below, it's a bit more cleanly implemented?
It still has the branch overhead per memory barrier, but I would not
worry about that too much.

diff --git a/arch/arch-sh.h b/arch/arch-sh.h
index 08c5fb3..ef4ee03 100644
--- a/arch/arch-sh.h
+++ b/arch/arch-sh.h
@@ -22,13 +22,38 @@
 
 #define nop             __asm__ __volatile__ ("nop": : :"memory")
 
-#if defined(__SH4A__)
-#define	mb()		__asm__ __volatile__ ("synco": : :"memory")
-#else
-#define mb()		__asm__ __volatile__ (" " : : : "memory")
-#endif
+#define mb()								\
+	do {								\
+		if (arch_flags & ARCH_FLAG_1)				\
+			__asm__ __volatile__ ("synco": : :"memory");	\
+		else							\
+			__asm__ __volatile__ (" " : : : "memory");	\
+	} while (0)
 
 #define read_barrier()	mb()
 #define write_barrier()	mb()
 
+#define CPU_HAS_LLSC	0x0040
+
+static inline int arch_init(char *envp[])
+{
+	Elf32_auxv_t *auxv;
+
+	while (*envp++ != NULL)
+		;
+
+	for (auxv = (Elf32_auxv_t *) envp; auxv->a_type != AT_NULL; auxv++) {
+		if (auxv->a_type == AT_HWCAP) {
+			if (auxv->a_un.a_val & CPU_HAS_LLSC) {
+				arch_flags |= ARCH_FLAG_1;
+				break;
+			}
+		}
+	}
+
+	return 0;
+}
+
+#define ARCH_HAVE_INIT
+
 #endif
diff --git a/arch/arch.h b/arch/arch.h
index 8cafa11..16f4c3a 100644
--- a/arch/arch.h
+++ b/arch/arch.h
@@ -58,4 +58,18 @@ enum {
 #include "../lib/ffz.h"
 #endif
 
+#ifndef ARCH_HAVE_INIT
+static inline int arch_init(char *envp[])
+{
+	return 0;
+}
+#endif
+
+enum {
+	ARCH_FLAG_1	= 1 << 0,
+	ARCH_FLAG_2	= 1 << 1,
+	ARCH_FLAG_3	= 1 << 2,
+	ARCH_FLAG_4	= 1 << 3,
+};
+
 #endif
diff --git a/fio.c b/fio.c
index 7396421..9c1bed3 100644
--- a/fio.c
+++ b/fio.c
@@ -70,6 +70,8 @@ static pthread_t disk_util_thread;
 static struct flist_head *cgroup_list;
 static char *cgroup_mnt;
 
+unsigned long arch_flags = 0;
+
 struct io_log *agg_io_log[2];
 
 #define TERMINATE_ALL		(-1)
@@ -1690,10 +1692,12 @@ static void run_threads(void)
 	fio_unpin_memory();
 }
 
-int main(int argc, char *argv[])
+int main(int argc, char *argv[], char *envp[])
 {
 	long ps;
 
+	arch_init(envp);
+
 	sinit();
 	init_rand(&__fio_rand_state);
 

-- 
Jens Axboe