From: David Miller <davem@davemloft.net>
To: andreas@gaisler.com
Cc: libc-alpha@sourceware.org, adhemerval.zanella@linaro.org,
carlos@redhat.com, triegel@redhat.com, software@gaisler.com
Subject: Re: [RFC][PATCH 2/2] sparc32: Use cas for atomic_* operations and use general pthread_barrier_wait
Date: Fri, 04 Nov 2016 18:44:00 -0000 [thread overview]
Message-ID: <20161104.144427.831418313476119230.davem@davemloft.net> (raw)
In-Reply-To: <20161104.143710.2239577261242146927.davem@davemloft.net>
From: David Miller <davem@davemloft.net>
Date: Fri, 04 Nov 2016 14:37:10 -0400 (EDT)
> From: Andreas Larsson <andreas@gaisler.com>
> Date: Tue, 1 Nov 2016 16:07:47 +0100
>
>> This uses the CASA compare and swap with user space data access ASI 0xa
>> that is present on many LEON3 and LEON4 systems and that is implied by
>> gcc's -mcpu=leon3.
>>
>> The CASA instruction is used not only for atomic compare and exchange
>> functions, but also atomic exchange functions and atomic write
>> functions. This is to allow the OS kernel to emulate that instruction on
>> systems where it is missing and to get atomicity between all atomic
>> writing functions without having to resort to stop all CPU:s in an SMP
>> system.
>
> Ok, this is fine. I'll work on the instruction emulation code for the
> kernel side.
Actually, this might cause some problems actually.
We don't always have access to a proper _dl_hwcap value. Which means
that we will emit the LEON CAS sometimes when running on a v9 chip
which will not work properly.
I need to think about this a bit more.
Probably what we need to do is have three cases:
1) We explicitly know we are on a v9 chip via dl_hwcap, emit v9 CAS
2) We explicitly know we are on a v8 LEON chip via dl_hwcap, emit LEON CAS
3) Else, we emit a special trap instruction which the kernel fixes up
I think this is necessary because we cannot attempt to execute one of
the two CAS cases on the opposing CAS cpu type.
next prev parent reply other threads:[~2016-11-04 18:44 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-01 15:08 [RFC][PATCH 0/2] Make sparcv8 work again on cas enabled hardware Andreas Larsson
2016-11-01 15:08 ` [RFC][PATCH 2/2] sparc32: Use cas for atomic_* operations and use general pthread_barrier_wait Andreas Larsson
2016-11-04 18:37 ` David Miller
2016-11-04 18:44 ` David Miller [this message]
2016-11-01 15:08 ` [RFC][PATCH 1/2] sparc32: Mark sendmsg and recvmsg system calls as unsupported Andreas Larsson
2016-11-01 17:28 ` Adhemerval Zanella
2016-11-02 11:38 ` Andreas Larsson
2016-11-02 12:49 ` Adhemerval Zanella
2016-11-04 18:36 ` David Miller
2016-11-01 16:00 ` [RFC][PATCH 0/2] Make sparcv8 work again on cas enabled hardware Torvald Riegel
2016-11-01 16:09 ` David Miller
2016-11-01 16:46 ` Torvald Riegel
2016-11-01 16:51 ` David Miller
2016-11-02 10:05 ` Torvald Riegel
2016-11-02 11:29 ` Andreas Larsson
2016-11-02 15:32 ` David Miller
2016-11-02 22:33 ` Torvald Riegel
2016-11-03 2:52 ` David Miller
2016-11-03 15:39 ` Torvald Riegel
2016-11-03 17:22 ` David Miller
2016-11-03 18:41 ` Adhemerval Zanella
2016-11-03 20:33 ` David Miller
2016-11-03 21:29 ` Adhemerval Zanella
2016-11-03 22:25 ` Torvald Riegel
2016-11-04 10:28 ` Andreas Larsson
2016-11-04 15:23 ` David Miller
2016-11-04 13:55 ` Richard Henderson
2016-11-04 15:31 ` David Miller
2016-11-04 16:10 ` Richard Henderson
2016-11-04 14:04 ` Richard Henderson
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