linux-kernel - [PATCH] kbuild: speed up checksyscalls.sh

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Date:   Thu,  1 Jun 2017 16:57:07 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Michal Marek <mmarek@...e.com>, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, sam@...nborg.org,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH] kbuild: speed up checksyscalls.sh

checksyscalls.sh is run at every "make" run while building the kernel,
even if no files have changed. I looked at where we spend time in
a trivial empty rebuild and found checksyscalls.sh to be a source
of noticeable overhead, as it spawns a lot of child processes just
to call 'cat' copying from stdin to stdout, once for each of the
over 400 x86 syscalls.

Using a shell-builtin (echo) instead of the external command gives
us a 13x speedup:

    Before		   After
real	0m1.018s       real	0m0.077s
user	0m0.068s       user	0m0.048s
sys	0m0.156s       sys	0m0.024s

The time it took to rebuild a single file on my machine dropped
from 5.5 seconds to 4.5 seconds.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 scripts/checksyscalls.sh | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/scripts/checksyscalls.sh b/scripts/checksyscalls.sh
index 0cce56da3706..b8c9d2b04ffc 100755
--- a/scripts/checksyscalls.sh
+++ b/scripts/checksyscalls.sh
@@ -231,15 +231,12 @@ EOF
 }
 
 syscall_list() {
-    grep '^[0-9]' "$1" | sort -n | (
+    grep '^[0-9]' "$1" | sort -n |
 	while read nr abi name entry ; do
-	    cat <<EOF
-#if !defined(__NR_${name}) && !defined(__IGNORE_${name})
-#warning syscall ${name} not implemented
-#endif
-EOF
+		echo "#if !defined(__NR_${name}) && !defined(__IGNORE_${name})"
+		echo "#warning syscall ${name} not implemented"
+		echo "#endif"
 	done
-    )
 }
 
 (ignore_list && syscall_list $(dirname $0)/../arch/x86/entry/syscalls/syscall_32.tbl) | \
-- 
2.9.0