From: Vincenzo Frascino <vincenzo.frascino@arm.com> To: Arnd Bergmann <arnd@arndb.de>, Thomas Gleixner <tglx@linutronix.de> Cc: linux-arch <linux-arch@vger.kernel.org>, Catalin Marinas <catalin.marinas@arm.com>, Daniel Lezcano <daniel.lezcano@linaro.org>, Will Deacon <will.deacon@arm.com>, Russell King - ARM Linux <linux@armlinux.org.uk>, Ralf Baechle <ralf@linux-mips.org>, Mark Salyzyn <salyzyn@android.com>, Paul Burton <paul.burton@mips.com>, Peter Collingbourne <pcc@google.com>, Linux ARM <linux-arm-kernel@lists.infradead.org> Subject: Re: [PATCH v2 06/28] kernel: Define gettimeofday vdso common code Date: Tue, 11 Dec 2018 14:02:59 +0000 [thread overview] Message-ID: <f374ad0f-18a8-d66e-00fa-cba4f25ed540@arm.com> (raw) In-Reply-To: <CAK8P3a1hmsf2CKWfQ60aUQMoC1YxWhkRKY3GBRusGnQ2cDCJpQ@mail.gmail.com> On 30/11/2018 14:29, Arnd Bergmann wrote: > On Thu, Nov 29, 2018 at 11:12 PM Thomas Gleixner <tglx@linutronix.de> wrote: >> On Thu, 29 Nov 2018, Vincenzo Frascino wrote: >>> +if HAVE_GENERIC_VDSO >>> + >>> +config GENERIC_GETTIMEOFDAY >>> + bool >>> + help >>> + This is a generic implementation of gettimeofday vdso. >>> + Each architecture that enables this feature has to >>> + provide the fallback implementation. >>> + >>> +config GENERIC_VDSO_32 >>> + bool >>> + depends on GENERIC_GETTIMEOFDAY && !64BIT >>> + help >>> + This config option helps to avoid possible performance issues >>> + in 32 bit only architectures. >>> + >>> +config HAVE_ARCH_TIMER >>> + bool >>> + depends on GENERIC_GETTIMEOFDAY >>> + help >>> + Select this configuration option if the architecture has an arch >>> + timer. >> >> Please don't add code which is architecture specific to the generic >> implementation. There is really no reason to make ARCH_TIMER special. > > I think it's just unfortunate naming based on what arm64 had, but > conceptually it does the right thing, and just disable the clock_gettime > fastpath on kernel builds that never have access to a clocksource > from user space. > I agree with Arnd here, that was the spirit of this option. I will find a better name in v3. >>> +static notrace int __cvdso_clock_getres(clockid_t clock_id, >>> + struct __vdso_timespec *res) >>> +{ >>> + u64 ns; >>> + >>> + if (!__arch_valid_arg(res)) >>> + return -EFAULT; >>> + >>> + if (clock_id == CLOCK_REALTIME || >>> + clock_id == CLOCK_TAI || >>> + clock_id == CLOCK_BOOTTIME || >>> + clock_id == CLOCK_MONOTONIC || >>> + clock_id == CLOCK_MONOTONIC_RAW) >>> + ns = MONOTONIC_RES_NSEC; >> >> This is wrong. You cannot unconditionally set that. See what the syscall >> based version does. You always need to verify that the syscall version and >> the vdso version return the same information and not something randomly >> different. > > Do you think we actually need the fastpath here? If not, the > easy way to do it would be to always fall back to calling > the syscall based version. Or was this originally added > to deal with the syscall and vdso clock_gettime having > different resolutions (which would sound like a bad idea, but > might have to stay for compatibility)? > Running ./vdsotest-bench on getres, these are the results: clock-getres-monotonic: syscall: 679 nsec/call clock-getres-monotonic: libc: 701 nsec/call (using syscall) clock-getres-monotonic: vdso: 14 nsec/call hence I think the fastpath for getres seems justified. > Arnd > -- Regards, Vincenzo
WARNING: multiple messages have this Message-ID (diff)
From: Vincenzo Frascino <vincenzo.frascino@arm.com> To: Arnd Bergmann <arnd@arndb.de>, Thomas Gleixner <tglx@linutronix.de> Cc: linux-arch <linux-arch@vger.kernel.org>, Linux ARM <linux-arm-kernel@lists.infradead.org>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Russell King - ARM Linux <linux@armlinux.org.uk>, Ralf Baechle <ralf@linux-mips.org>, Paul Burton <paul.burton@mips.com>, Daniel Lezcano <daniel.lezcano@linaro.org>, Mark Salyzyn <salyzyn@android.com>, Peter Collingbourne <pcc@google.com> Subject: Re: [PATCH v2 06/28] kernel: Define gettimeofday vdso common code Date: Tue, 11 Dec 2018 14:02:59 +0000 [thread overview] Message-ID: <f374ad0f-18a8-d66e-00fa-cba4f25ed540@arm.com> (raw) Message-ID: <20181211140259.ABsWIMI_TrT1zHC-Eepinb22tOUMykYFil3MJirVYGY@z> (raw) In-Reply-To: <CAK8P3a1hmsf2CKWfQ60aUQMoC1YxWhkRKY3GBRusGnQ2cDCJpQ@mail.gmail.com> On 30/11/2018 14:29, Arnd Bergmann wrote: > On Thu, Nov 29, 2018 at 11:12 PM Thomas Gleixner <tglx@linutronix.de> wrote: >> On Thu, 29 Nov 2018, Vincenzo Frascino wrote: >>> +if HAVE_GENERIC_VDSO >>> + >>> +config GENERIC_GETTIMEOFDAY >>> + bool >>> + help >>> + This is a generic implementation of gettimeofday vdso. >>> + Each architecture that enables this feature has to >>> + provide the fallback implementation. >>> + >>> +config GENERIC_VDSO_32 >>> + bool >>> + depends on GENERIC_GETTIMEOFDAY && !64BIT >>> + help >>> + This config option helps to avoid possible performance issues >>> + in 32 bit only architectures. >>> + >>> +config HAVE_ARCH_TIMER >>> + bool >>> + depends on GENERIC_GETTIMEOFDAY >>> + help >>> + Select this configuration option if the architecture has an arch >>> + timer. >> >> Please don't add code which is architecture specific to the generic >> implementation. There is really no reason to make ARCH_TIMER special. > > I think it's just unfortunate naming based on what arm64 had, but > conceptually it does the right thing, and just disable the clock_gettime > fastpath on kernel builds that never have access to a clocksource > from user space. > I agree with Arnd here, that was the spirit of this option. I will find a better name in v3. >>> +static notrace int __cvdso_clock_getres(clockid_t clock_id, >>> + struct __vdso_timespec *res) >>> +{ >>> + u64 ns; >>> + >>> + if (!__arch_valid_arg(res)) >>> + return -EFAULT; >>> + >>> + if (clock_id == CLOCK_REALTIME || >>> + clock_id == CLOCK_TAI || >>> + clock_id == CLOCK_BOOTTIME || >>> + clock_id == CLOCK_MONOTONIC || >>> + clock_id == CLOCK_MONOTONIC_RAW) >>> + ns = MONOTONIC_RES_NSEC; >> >> This is wrong. You cannot unconditionally set that. See what the syscall >> based version does. You always need to verify that the syscall version and >> the vdso version return the same information and not something randomly >> different. > > Do you think we actually need the fastpath here? If not, the > easy way to do it would be to always fall back to calling > the syscall based version. Or was this originally added > to deal with the syscall and vdso clock_gettime having > different resolutions (which would sound like a bad idea, but > might have to stay for compatibility)? > Running ./vdsotest-bench on getres, these are the results: clock-getres-monotonic: syscall: 679 nsec/call clock-getres-monotonic: libc: 701 nsec/call (using syscall) clock-getres-monotonic: vdso: 14 nsec/call hence I think the fastpath for getres seems justified. > Arnd > -- Regards, Vincenzo
next prev parent reply other threads:[~2018-12-11 14:02 UTC|newest] Thread overview: 100+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-11-29 17:05 [PATCH v2 00/28] Unify vDSOs across more architectures Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 01/28] kernel: Standardize vdso_datapage Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 22:39 ` Thomas Gleixner 2018-11-29 22:39 ` Thomas Gleixner 2018-12-11 13:22 ` Vincenzo Frascino 2018-12-11 13:22 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 02/28] kernel: Add Monotonic boot time support Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 03/28] kernel: Add International Atomic Time support Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 04/28] kernel: Add masks support for Raw and NTP time Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 22:41 ` Thomas Gleixner 2018-11-29 22:41 ` Thomas Gleixner 2018-12-11 13:24 ` Vincenzo Frascino 2018-12-11 13:24 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 05/28] kernel: Add clock_mode support Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 06/28] kernel: Define gettimeofday vdso common code Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 20:42 ` Arnd Bergmann 2018-11-29 20:42 ` Arnd Bergmann 2018-12-11 13:39 ` Vincenzo Frascino 2018-12-11 13:39 ` Vincenzo Frascino 2018-12-11 21:41 ` Arnd Bergmann 2018-12-11 21:41 ` Arnd Bergmann 2018-12-13 9:46 ` Vincenzo Frascino 2018-12-13 9:46 ` Vincenzo Frascino 2018-11-29 22:11 ` Thomas Gleixner 2018-11-29 22:11 ` Thomas Gleixner 2018-11-30 14:29 ` Arnd Bergmann 2018-11-30 14:29 ` Arnd Bergmann 2018-12-11 14:02 ` Vincenzo Frascino [this message] 2018-12-11 14:02 ` Vincenzo Frascino 2018-12-07 17:53 ` Will Deacon 2018-12-07 17:53 ` Will Deacon 2019-02-08 17:35 ` Will Deacon 2019-02-08 17:35 ` Will Deacon 2019-02-08 19:28 ` Thomas Gleixner 2019-02-08 19:28 ` Thomas Gleixner 2019-02-08 19:30 ` Thomas Gleixner 2019-02-08 19:30 ` Thomas Gleixner 2019-02-13 17:04 ` Will Deacon 2019-02-13 17:04 ` Will Deacon 2019-02-13 19:35 ` Thomas Gleixner 2019-02-13 19:35 ` Thomas Gleixner 2019-02-13 17:05 ` Will Deacon 2019-02-13 17:05 ` Will Deacon 2018-12-11 13:54 ` Vincenzo Frascino 2018-12-11 13:54 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 07/28] arm64: Build vDSO with -ffixed-x18 Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 08/28] arm64: Substitute gettimeofday with C implementation Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 09/28] arm64: compat: Alloc separate pages for vectors and sigpage Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 10/28] arm64: compat: Split kuser32 Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 11/28] arm64: compat: Refactor aarch32_alloc_vdso_pages() Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 12/28] arm64: compat: Add KUSER_HELPERS config option Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 13/28] arm64: compat: Add missing syscall numbers Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 14/28] arm64: compat: Expose signal related structures Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 15/28] arm64: compat: Generate asm offsets for signals Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 16/28] lib: vdso: Add compat support Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 17/28] arm64: compat: Add vDSO Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 18/28] arm64: Refactor vDSO code Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 19/28] arm64: compat: vDSO setup for compat layer Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 20/28] arm64: elf: vDSO code page discovery Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 21/28] arm64: compat: Get sigreturn trampolines from vDSO Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 22/28] arm64: Add vDSO compat support Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 23/28] arm64: Enable compat vDSO support Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 24/28] arm: Add support for generic vDSO Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-12-10 22:13 ` Mark Salyzyn 2018-12-10 22:13 ` Mark Salyzyn 2018-12-11 14:15 ` Vincenzo Frascino 2018-12-11 14:15 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 25/28] mips: Introduce vdso_direct Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 26/28] clock: csrc-4k: Add support for vdso_direct Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 27/28] clock: gic-timer: " Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino 2018-11-29 17:05 ` [PATCH v2 28/28] mips: Add support for generic vDSO Vincenzo Frascino 2018-11-29 17:05 ` Vincenzo Frascino
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=f374ad0f-18a8-d66e-00fa-cba4f25ed540@arm.com \ --to=vincenzo.frascino@arm.com \ --cc=arnd@arndb.de \ --cc=catalin.marinas@arm.com \ --cc=daniel.lezcano@linaro.org \ --cc=linux-arch@vger.kernel.org \ --cc=linux-arm-kernel@lists.infradead.org \ --cc=linux@armlinux.org.uk \ --cc=paul.burton@mips.com \ --cc=pcc@google.com \ --cc=ralf@linux-mips.org \ --cc=salyzyn@android.com \ --cc=tglx@linutronix.de \ --cc=will.deacon@arm.com \ /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: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).