On Thu, Sep 06, 2018 at 04:24:59PM +0200, Arnd Bergmann wrote:
> On Wed, Sep 5, 2018 at 2:08 PM Guo Ren <ren_guo@xxxxxxxxx> wrote:
>
> > --- /dev/null
> > +++ b/arch/csky/abiv1/memset.c
> > @@ -0,0 +1,38 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +// Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd.
> > +#include <linux/types.h>
> > +
> > +void *memset(void *dest, int c, size_t l)
> > +{
> > + char *d = dest;
> > + int ch = c;
> > + int tmp;
> > +
> > + if ((long)d & 0x3)
> > + while (l--) *d++ = ch;
> > + else {
> > + ch &= 0xff;
> > + tmp = (ch | ch << 8 | ch << 16 | ch << 24);
> > +
> > + while (l >= 16) {
> > + *(((long *)d)) = tmp;
> > + *(((long *)d)+1) = tmp;
> > + *(((long *)d)+2) = tmp;
> > + *(((long *)d)+3) = tmp;
> > + l -= 16;
> > + d += 16;
> > + }
> > +
> > + while (l > 3) {
> > + *(((long *)d)) = tmp;
> > + d = d + 4;
> > + l -= 4;
> > + }
> > +
> > + while (l) {
> > + *d++ = ch;
> > + l--;
> > + }
> > + }
> > + return dest;
> > +}
>
> I see that we have a trivial memset() implementation in lib/string.c, but yours
> seems to be better optimized. Where did you get it from?
We write it for our ck610 to improve the performance, but I think a lot
of other arch done it in asm style.
> Is this a version
> that works particularly well on C-Sky, or is this a generic optimized memset
> that others could use as well?
We only test it on C-SKY, but I think it will also work better on other
arch CPU than current lib/string.c memset implement.
I see that in lib/string.c:
void *memset(void *s, int c, size_t count)
{
char *xs = s;
while (count--)
*xs++ = c;
return s;
}
The most problem is "char *xs;" and it will cause "st.b" in asm.
"st.b" is very slow.
Our key improvement is:
> > + *(((long *)d)) = tmp;
> > + *(((long *)d)+1) = tmp;
> > + *(((long *)d)+2) = tmp;
> > + *(((long *)d)+3) = tmp;
It will cause SOC AXI burst transfer.
> In the latter case, we could add it to
> lib/string.c and let architectures select it in place of the triivial version.
Good idea.
Guo Ren
