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From: Alistair Francis <alistair23@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: "André Almeida" <andrealmeid@collabora.com>,
	"Alistair Francis" <alistair.francis@opensource.wdc.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	linux-riscv <linux-riscv@lists.infradead.org>,
	"Namhyung Kim" <namhyung@kernel.org>,
	"Jiri Olsa" <jolsa@redhat.com>,
	linux-perf-users@vger.kernel.org,
	"Alexander Shishkin" <alexander.shishkin@linux.intel.com>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Arnaldo Carvalho de Melo" <acme@kernel.org>,
	"Davidlohr Bueso" <dave@stgolabs.net>,
	"Darren Hart" <dvhart@infradead.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Atish Patra" <atish.patra@wdc.com>,
	"Alistair Francis" <alistair.francis@wdc.com>
Subject: Re: [PATCH v3 2/2] perf bench: Add support for 32-bit systems with 64-bit time_t
Date: Fri, 24 Sep 2021 14:34:56 +1000	[thread overview]
Message-ID: <CAKmqyKM3vy_Ob1a0=cEi_Efi6_VVAa8YfMb6+rOt3fQK_TTcmw@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a3x_EyCiPDpMK54y=Rtm-Wb08ym2TNiuAZgXhYrThcWTw@mail.gmail.com>

On Tue, Sep 21, 2021 at 6:08 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Tue, Sep 21, 2021 at 12:47 AM André Almeida
> <andrealmeid@collabora.com> wrote:
> >
> > #if defined(__i386__) || __TIMESIZE == 32
> > # define NR_gettime64 __NR_clock_gettime64
> > #else
> > # define NR_gettime64 __NR_clock_gettime
> > #endif
> >
> > struct timespec64 {
> >         long long tv_sec;       /* seconds */
> >         long long tv_nsec;      /* nanoseconds */
> > };
> >
> > int gettime64(clock_t clockid, struct timespec64 *tv)
> > {
> >         return syscall(NR_gettime64, clockid, tv);
> > }
> >
> > Then we can just use &timeout at __NR_futex_time64 for 32bit arch and at
> > __NR_futex for 64bit arch.
>
> This is still broken when you disable CONFIG_COMPAT_32BIT_TIME,
> which disables all system calls that take time32 arguments.
>
> > This might be a simpler solution to the problem that you are facing but
> > I'm not entirely sure. Also, futex's selftests do use the timeout
> > argument and I think that they also won't compile in 32-bit RISC-V, so
> > maybe we can start from there so we can actually test the timeout
> > argument and check if it's working.
>
> I would love to see the wrapper that Alistair wrote as part of some kernel
> uapi header provided to user space. futex is used by tons of applications,
> and we never had a library abstraction for it, so everyone has to do these
> by hand, and they all get them slightly wrong in different ways.
>
> We normally don't do this in kernel headers, but I think the benefits
> would be far greater compared to today's situation.

I'm happy to prepare a patch, if others are on board with it being accepted.

Alistair

>
>       Arnd

WARNING: multiple messages have this Message-ID
From: Alistair Francis <alistair23@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: "André Almeida" <andrealmeid@collabora.com>,
	"Alistair Francis" <alistair.francis@opensource.wdc.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	linux-riscv <linux-riscv@lists.infradead.org>,
	"Namhyung Kim" <namhyung@kernel.org>,
	"Jiri Olsa" <jolsa@redhat.com>,
	linux-perf-users@vger.kernel.org,
	"Alexander Shishkin" <alexander.shishkin@linux.intel.com>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Arnaldo Carvalho de Melo" <acme@kernel.org>,
	"Davidlohr Bueso" <dave@stgolabs.net>,
	"Darren Hart" <dvhart@infradead.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Atish Patra" <atish.patra@wdc.com>,
	"Alistair Francis" <alistair.francis@wdc.com>
Subject: Re: [PATCH v3 2/2] perf bench: Add support for 32-bit systems with 64-bit time_t
Date: Fri, 24 Sep 2021 14:34:56 +1000	[thread overview]
Message-ID: <CAKmqyKM3vy_Ob1a0=cEi_Efi6_VVAa8YfMb6+rOt3fQK_TTcmw@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a3x_EyCiPDpMK54y=Rtm-Wb08ym2TNiuAZgXhYrThcWTw@mail.gmail.com>

On Tue, Sep 21, 2021 at 6:08 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Tue, Sep 21, 2021 at 12:47 AM André Almeida
> <andrealmeid@collabora.com> wrote:
> >
> > #if defined(__i386__) || __TIMESIZE == 32
> > # define NR_gettime64 __NR_clock_gettime64
> > #else
> > # define NR_gettime64 __NR_clock_gettime
> > #endif
> >
> > struct timespec64 {
> >         long long tv_sec;       /* seconds */
> >         long long tv_nsec;      /* nanoseconds */
> > };
> >
> > int gettime64(clock_t clockid, struct timespec64 *tv)
> > {
> >         return syscall(NR_gettime64, clockid, tv);
> > }
> >
> > Then we can just use &timeout at __NR_futex_time64 for 32bit arch and at
> > __NR_futex for 64bit arch.
>
> This is still broken when you disable CONFIG_COMPAT_32BIT_TIME,
> which disables all system calls that take time32 arguments.
>
> > This might be a simpler solution to the problem that you are facing but
> > I'm not entirely sure. Also, futex's selftests do use the timeout
> > argument and I think that they also won't compile in 32-bit RISC-V, so
> > maybe we can start from there so we can actually test the timeout
> > argument and check if it's working.
>
> I would love to see the wrapper that Alistair wrote as part of some kernel
> uapi header provided to user space. futex is used by tons of applications,
> and we never had a library abstraction for it, so everyone has to do these
> by hand, and they all get them slightly wrong in different ways.
>
> We normally don't do this in kernel headers, but I think the benefits
> would be far greater compared to today's situation.

I'm happy to prepare a patch, if others are on board with it being accepted.

Alistair

>
>       Arnd

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  parent reply	other threads:[~2021-09-24  4:35 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-17  6:10 [PATCH v3 1/2] perf benchmark: Call the futex syscall from a function Alistair Francis
2021-09-17  6:10 ` Alistair Francis
2021-09-17  6:10 ` [PATCH v3 2/2] perf bench: Add support for 32-bit systems with 64-bit time_t Alistair Francis
2021-09-17  6:10   ` Alistair Francis
2021-09-17  7:33   ` Arnd Bergmann
2021-09-17  7:33     ` Arnd Bergmann
2021-09-17 18:33   ` Davidlohr Bueso
2021-09-17 18:33     ` Davidlohr Bueso
2021-09-20 22:47   ` André Almeida
2021-09-20 22:47     ` André Almeida
2021-09-21  8:08     ` Arnd Bergmann
2021-09-21  8:08       ` Arnd Bergmann
2021-09-21 23:06       ` André Almeida
2021-09-21 23:06         ` André Almeida
2021-09-22 11:26         ` Arnd Bergmann
2021-09-22 11:26           ` Arnd Bergmann
2021-09-22 11:27         ` Arnd Bergmann
2021-09-22 11:27           ` Arnd Bergmann
2021-09-24  4:34       ` Alistair Francis [this message]
2021-09-24  4:34         ` Alistair Francis
2021-09-24  4:34     ` Alistair Francis
2021-09-24  4:34       ` Alistair Francis
2021-09-26 21:32       ` André Almeida
2021-09-26 21:32         ` André Almeida
2021-09-17 18:21 ` [PATCH v3 1/2] perf benchmark: Call the futex syscall from a function Davidlohr Bueso
2021-09-17 18:21   ` Davidlohr Bueso

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