Date: Tue, 2 Oct 2018 13:51:11 +0200 From: Sebastian Huber <sebastian.huber@embedded-brains.de> To: FreeBSD <freebsd-hackers@freebsd.org> Subject: m_copydata() with overlapping data? Message-ID: <6c801b04-6e07-3122-868c-20810e795aa7@embedded-brains.de>
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Hello,
I investigate currently a performance issue on a Microchip ATSAME70Q21=20
(ARM Cortex-M7). The Newlib C-library has specialized routines for=20
memcpy(), but not for memmove(). I noticed that m_copydata() uses=20
bcopy() internally. According to the man page bcopy() is capable to deal=20
with overlapping memory regions. Is this also a requirement for=20
m_copydata() or could we use memcpy() here? For example:
diff --git a/freebsd/sys/kern/uipc_mbuf.c b/freebsd/sys/kern/uipc_mbuf.c
index 185d14a0..00dcd975 100644
--- a/freebsd/sys/kern/uipc_mbuf.c
+++ b/freebsd/sys/kern/uipc_mbuf.c
@@ -593,7 +593,7 @@ m_copydata(const struct mbuf *m, int off, int len,=20
caddr_t cp)
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 while (len > 0) {
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0 KASSERT(m !=3D NULL, ("m_copydata, length > size of mb=
uf=20
chain"));
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0 count =3D min(m->m_len - off, len);
-=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0 bcopy(mtod(m, caddr_t) + off, cp, count);
+=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0 cp =3D memcpy(cp, mtod(m, caddr_t) + off, count);
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0 len -=3D count;
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0 cp +=3D count;
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0 off =3D 0;
Maybe this should be mentioned in the man page:
https://www.freebsd.org/cgi/man.cgi?query=3Dm_copydata
--=20
Sebastian Huber, embedded brains GmbH
Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone : +49 89 189 47 41-16
Fax : +49 89 189 47 41-09
E-Mail : sebastian.huber@embedded-brains.de
PGP : Public key available on request.
Diese Nachricht ist keine gesch=C3=A4ftliche Mitteilung im Sinne des EHUG=
.
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