From: Christophe Leroy <christophe.leroy@c-s.fr> To: Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paulus@samba.org>, Michael Ellerman <mpe@ellerman.id.au>, nathanl@linux.ibm.com, arnd@arndb.de, tglx@linutronix.de, vincenzo.frascino@arm.com, luto@kernel.org Cc: x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org Subject: [RFC PATCH v4 10/11] lib: vdso: Allow arches to override the ns shift operation Date: Thu, 16 Jan 2020 17:58:34 +0000 (UTC) Message-ID: <c8ce9baaef0dc7273e4bcc31f353b17b655113d1.1579196675.git.christophe.leroy@c-s.fr> (raw) In-Reply-To: <cover.1579196675.git.christophe.leroy@c-s.fr> On powerpc/32, GCC (8.1) generates pretty bad code for the ns >>= vd->shift operation taking into account that the shift is always < 32 and the upper part of the result is likely to be nul. GCC makes reversed assumptions considering the shift to be likely >= 32 and the upper part to be like not nul. unsigned long long shift(unsigned long long x, unsigned char s) { return x >> s; } results in: 00000018 <shift>: 18: 35 25 ff e0 addic. r9,r5,-32 1c: 41 80 00 10 blt 2c <shift+0x14> 20: 7c 64 4c 30 srw r4,r3,r9 24: 38 60 00 00 li r3,0 28: 4e 80 00 20 blr 2c: 54 69 08 3c rlwinm r9,r3,1,0,30 30: 21 45 00 1f subfic r10,r5,31 34: 7c 84 2c 30 srw r4,r4,r5 38: 7d 29 50 30 slw r9,r9,r10 3c: 7c 63 2c 30 srw r3,r3,r5 40: 7d 24 23 78 or r4,r9,r4 44: 4e 80 00 20 blr Even when forcing the shift with an &= 31, it still considers the shift as likely >= 32. Define a vdso_shift_ns() macro that can be overriden by arches. Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr> --- lib/vdso/gettimeofday.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c index 724b45c3e8ac..9ba92058cfd7 100644 --- a/lib/vdso/gettimeofday.c +++ b/lib/vdso/gettimeofday.c @@ -39,6 +39,13 @@ u64 vdso_calc_delta(u64 cycles, u64 last, u64 mask, u32 mult) } #endif +#ifndef vdso_shift_ns +static __always_inline u64 vdso_shift_ns(u64 ns, unsigned long shift) +{ + return ns >> shift; +} +#endif + #ifndef __arch_vdso_hres_capable static inline bool __arch_vdso_hres_capable(void) { @@ -148,7 +155,7 @@ static __always_inline int do_hres(const struct vdso_data *vd, clockid_t clk, ns = vdso_ts->nsec; last = vd->cycle_last; ns += vdso_calc_delta(cycles, last, vd->mask, vd->mult); - ns >>= vd->shift; + ns = vdso_shift_ns(ns, vd->shift); sec = vdso_ts->sec; } while (unlikely(vdso_read_retry(vd, seq))); -- 2.13.3
next prev parent reply index Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-01-16 17:58 [RFC PATCH v4 00/11] powerpc: switch VDSO to C implementation Christophe Leroy 2020-01-16 17:58 ` [RFC PATCH v4 01/11] powerpc/64: Don't provide time functions in compat VDSO32 Christophe Leroy 2020-01-16 17:58 ` [RFC PATCH v4 02/11] powerpc/vdso: Switch VDSO to generic C implementation Christophe Leroy 2020-01-16 17:58 ` [RFC PATCH v4 03/11] lib: vdso: only read hrtimer_res when needed in __cvdso_clock_getres() Christophe Leroy 2020-01-16 17:58 ` [RFC PATCH v4 04/11] powerpc/vdso: simplify __get_datapage() Christophe Leroy 2020-01-16 17:58 ` [RFC PATCH v4 05/11] lib: vdso: allow arches to provide vdso data pointer Christophe Leroy 2020-01-16 17:58 ` [RFC PATCH v4 06/11] powerpc/vdso: provide inline alternative to __get_datapage() Christophe Leroy 2020-01-16 17:58 ` [RFC PATCH v4 07/11] powerpc/vdso: provide vdso data pointer from the ASM caller Christophe Leroy 2020-01-16 17:58 ` [RFC PATCH v4 08/11] lib: vdso: allow fixed clock mode Christophe Leroy 2020-01-16 20:13 ` Thomas Gleixner 2020-01-16 20:19 ` Andy Lutomirski 2020-01-16 21:07 ` Thomas Gleixner 2020-01-16 17:58 ` [RFC PATCH v4 09/11] powerpc/vdso: override __arch_vdso_capable() Christophe Leroy 2020-01-16 17:58 ` Christophe Leroy [this message] 2020-01-16 19:47 ` [RFC PATCH v4 10/11] lib: vdso: Allow arches to override the ns shift operation Andy Lutomirski 2020-01-16 19:57 ` Thomas Gleixner 2020-01-16 20:20 ` Andy Lutomirski 2020-01-29 7:14 ` Thomas Gleixner 2020-01-29 7:26 ` Christophe Leroy 2020-01-16 17:58 ` [RFC PATCH v4 11/11] powerpc/32: provide vdso_shift_ns() Christophe Leroy 2020-01-17 8:58 ` [RFC PATCH v4 00/11] powerpc: switch VDSO to C implementation Segher Boessenkool 2020-01-17 9:26 ` Christophe Leroy 2020-01-20 14:56 ` Christophe Leroy 2020-01-20 15:19 ` Segher Boessenkool 2020-01-20 17:08 ` Christophe Leroy 2020-01-20 17:27 ` Segher Boessenkool
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=c8ce9baaef0dc7273e4bcc31f353b17b655113d1.1579196675.git.christophe.leroy@c-s.fr \ --to=christophe.leroy@c-s.fr \ --cc=arnd@arndb.de \ --cc=benh@kernel.crashing.org \ --cc=linux-arm-kernel@lists.infradead.org \ --cc=linux-kernel@vger.kernel.org \ --cc=linux-mips@vger.kernel.org \ --cc=linuxppc-dev@lists.ozlabs.org \ --cc=luto@kernel.org \ --cc=mpe@ellerman.id.au \ --cc=nathanl@linux.ibm.com \ --cc=paulus@samba.org \ --cc=tglx@linutronix.de \ --cc=vincenzo.frascino@arm.com \ --cc=x86@kernel.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
LinuxPPC-Dev Archive on lore.kernel.org Archives are clonable: git clone --mirror https://lore.kernel.org/linuxppc-dev/0 linuxppc-dev/git/0.git # If you have public-inbox 1.1+ installed, you may # initialize and index your mirror using the following commands: public-inbox-init -V2 linuxppc-dev linuxppc-dev/ https://lore.kernel.org/linuxppc-dev \ linuxppc-dev@lists.ozlabs.org linuxppc-dev@ozlabs.org public-inbox-index linuxppc-dev Example config snippet for mirrors Newsgroup available over NNTP: nntp://nntp.lore.kernel.org/org.ozlabs.lists.linuxppc-dev AGPL code for this site: git clone https://public-inbox.org/public-inbox.git