From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Gleixner Subject: [patch V2 08/11] x86/vdso: Replace the clockid switch case Date: Mon, 17 Sep 2018 14:45:41 +0200 Message-ID: <20180917130707.574315796__18329.8343945809$1537190312$gmane$org@linutronix.de> References: <20180917124533.329334911@linutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline; filename=x86-vdso--Replace-the-clockid-switch-case.patch List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: LKML Cc: Florian Weimer , Juergen Gross , Arnd Bergmann , Peter Zijlstra , x86@kernel.org, virtualization@lists.linux-foundation.org, Stephen Boyd , John Stultz , Andy Lutomirski , Paolo Bonzini , devel@linuxdriverproject.org, Matt Rickard List-Id: virtualization@lists.linuxfoundation.org Now that the time getter functions use the clockid as index into the storage array for the base time access, the switch case can be replaced. - Check for clockid >= MAX_CLOCKS and for negative clockid (CPU/FD) first and call the fallback function right away. - After establishing that clockid is < MAX_CLOCKS, convert the clockid to a bitmask - Check for the supported high resolution and coarse functions by anding the bitmask of supported clocks and check whether a bit is set. This completely avoids jump tables, reduces the number of conditionals and makes the VDSO extensible for other clock ids. Signed-off-by: Thomas Gleixner --- arch/x86/entry/vdso/vclock_gettime.c | 38 ++++++++++++++++------------------- 1 file changed, 18 insertions(+), 20 deletions(-) --- a/arch/x86/entry/vdso/vclock_gettime.c +++ b/arch/x86/entry/vdso/vclock_gettime.c @@ -239,29 +239,27 @@ notrace static void do_coarse(clockid_t notrace int __vdso_clock_gettime(clockid_t clock, struct timespec *ts) { - switch (clock) { - case CLOCK_REALTIME: - if (do_hres(CLOCK_REALTIME, ts) == VCLOCK_NONE) - goto fallback; - break; - case CLOCK_MONOTONIC: - if (do_hres(CLOCK_MONOTONIC, ts) == VCLOCK_NONE) - goto fallback; - break; - case CLOCK_REALTIME_COARSE: - do_coarse(CLOCK_REALTIME_COARSE, ts); - break; - case CLOCK_MONOTONIC_COARSE: - do_coarse(CLOCK_MONOTONIC_COARSE, ts); - break; - default: - goto fallback; - } + unsigned int msk; + + /* Sort out negative (CPU/FD) and invalid clocks */ + if (unlikely((unsigned int) clock >= MAX_CLOCKS)) + return vdso_fallback_gettime(clock, ts); - return 0; -fallback: + /* + * Convert the clockid to a bitmask and use it to check which + * clocks are handled in the VDSO directly. + */ + msk = 1U << clock; + if (likely(msk & VGTOD_HRES)) { + if (do_hres(clock, ts) != VCLOCK_NONE) + return 0; + } else if (msk & VGTOD_COARSE) { + do_coarse(clock, ts); + return 0; + } return vdso_fallback_gettime(clock, ts); } + int clock_gettime(clockid_t, struct timespec *) __attribute__((weak, alias("__vdso_clock_gettime")));