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| Started by | Arnd Bergmann <arnd@arndb.de> |
|---|---|
| First post | 2015-11-03 10:20 +0100 |
| Last post | 2015-11-04 22:50 +0100 |
| Articles | 3 — 3 participants |
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Re: [PATCH 2/5] do_div(): generic optimization for constant divisor on 32-bit machines Arnd Bergmann <arnd@arndb.de> - 2015-11-03 10:20 +0100
Re: [PATCH 2/5] do_div(): generic optimization for constant divisor on 32-bit machines Nicolas Pitre <nicolas.pitre@linaro.org> - 2015-11-04 22:10 +0100
Re: [PATCH 2/5] do_div(): generic optimization for constant divisor on 32-bit machines Måns Rullgård <mans@mansr.com> - 2015-11-04 22:50 +0100
| From | Arnd Bergmann <arnd@arndb.de> |
|---|---|
| Date | 2015-11-03 10:20 +0100 |
| Subject | Re: [PATCH 2/5] do_div(): generic optimization for constant divisor on 32-bit machines |
| Message-ID | <qqFUZ-JW-3@gated-at.bofh.it> |
On Tuesday 03 November 2015 13:32:17 kbuild test robot wrote:
>
> net/can/bcm.c: In function 'bcm_proc_show':
> >> net/can/bcm.c:223:1: warning: the frame size of 1156 bytes is larger than 1024 bytes [-Wframe-larger-than=]
> }
Interesting, that is a lot of stack for a function that only has a couple
of local variables:
#define IFNAMSIZ 16
char ifname[IFNAMSIZ];
struct sock *sk = (struct sock *)m->private;
struct bcm_sock *bo = bcm_sk(sk);
struct bcm_op *op;
This is a parisc-allyesconfig kernel, so I assume that CONFIG_PROFILE_ALL_BRANCHES
is on, which instruments every 'if' in the kernel. If that causes problems,
we could decide to disable the do_div optimization whenever CONFIG_PROFILE_ALL_BRANCHES
is enabled.
Arnd
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| From | Nicolas Pitre <nicolas.pitre@linaro.org> |
|---|---|
| Date | 2015-11-04 22:10 +0100 |
| Subject | Re: [PATCH 2/5] do_div(): generic optimization for constant divisor on 32-bit machines |
| Message-ID | <qrdtE-5KP-7@gated-at.bofh.it> |
| In reply to | #1261324 |
On Tue, 3 Nov 2015, Arnd Bergmann wrote: > On Tuesday 03 November 2015 13:32:17 kbuild test robot wrote: > > > > net/can/bcm.c: In function 'bcm_proc_show': > > >> net/can/bcm.c:223:1: warning: the frame size of 1156 bytes is larger than 1024 bytes [-Wframe-larger-than=] > > } > > Interesting, that is a lot of stack for a function that only has a couple > of local variables: > > #define IFNAMSIZ 16 > char ifname[IFNAMSIZ]; > struct sock *sk = (struct sock *)m->private; > struct bcm_sock *bo = bcm_sk(sk); > struct bcm_op *op; > > > This is a parisc-allyesconfig kernel, so I assume that CONFIG_PROFILE_ALL_BRANCHES > is on, which instruments every 'if' in the kernel. If that causes problems, > we could decide to disable the do_div optimization whenever CONFIG_PROFILE_ALL_BRANCHES > is enabled. I have an ARM allyesconfig build here where that function needs a frame of 88 bytes only. And that is with my do_div optimization applied. With the do_div optimization turned off, the stack frame is still 88 bytes. Turning on CONFIG_PROFILE_ALL_BRANCHES makes the frame size to grow to 96 bytes. Keeping CONFIG_PROFILE_ALL_BRANCHES=y and activating the do_div optimization again, and the function frame size goes back to 88 bytes. So I wonder what parisc gcc could be doing with this code. Nicolas -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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| From | Måns Rullgård <mans@mansr.com> |
|---|---|
| Date | 2015-11-04 22:50 +0100 |
| Message-ID | <qre6m-5Zh-29@gated-at.bofh.it> |
| In reply to | #1262600 |
Nicolas Pitre <nicolas.pitre@linaro.org> writes: > On Tue, 3 Nov 2015, Arnd Bergmann wrote: > >> On Tuesday 03 November 2015 13:32:17 kbuild test robot wrote: >> > >> > net/can/bcm.c: In function 'bcm_proc_show': >> > >> net/can/bcm.c:223:1: warning: the frame size of 1156 bytes is larger than 1024 bytes [-Wframe-larger-than=] >> > } >> >> Interesting, that is a lot of stack for a function that only has a couple >> of local variables: >> >> #define IFNAMSIZ 16 >> char ifname[IFNAMSIZ]; >> struct sock *sk = (struct sock *)m->private; >> struct bcm_sock *bo = bcm_sk(sk); >> struct bcm_op *op; >> >> >> This is a parisc-allyesconfig kernel, so I assume that CONFIG_PROFILE_ALL_BRANCHES >> is on, which instruments every 'if' in the kernel. If that causes problems, >> we could decide to disable the do_div optimization whenever CONFIG_PROFILE_ALL_BRANCHES >> is enabled. > > I have an ARM allyesconfig build here where that function needs a frame > of 88 bytes only. And that is with my do_div optimization applied. > > With the do_div optimization turned off, the stack frame is still 88 > bytes. > > Turning on CONFIG_PROFILE_ALL_BRANCHES makes the frame size to grow to > 96 bytes. > > Keeping CONFIG_PROFILE_ALL_BRANCHES=y and activating the do_div > optimization again, and the function frame size goes back to 88 bytes. > > So I wonder what parisc gcc could be doing with this code. I've seen parisc gcc do many strange things. -- Måns Rullgård mans@mansr.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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