Re: [UNIKRAFT PATCH] include: Introduce uk/preemmpt.h

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

Hey Costin, hey Alexander,

a question from my side as clarification. I understand this is kind of an 
adopted concept from Linux. However, is it intended that interrupts do not 
count as preemption? When do I use uk_preempt_disable() and when 
lcpu_irqf_save()?
When scheduling is there, does this general header get a dependency to uksched? 
In such a case, shouldn't this header go to uksched and in ukring we include it 
as soon as uksched is selected?

Thanks,

Simon

On 23.07.20, 11:39, "Alexander Jung" <a.jung@xxxxxxxxxxx> wrote:

    This commit adds an additional header with two new methods:
    
     - preempt_disable()
     - preempt_enable()
    
    These methods enable and disable preemption by calling a memory
    barrier only.  Their names are derived from the Linux Kernel[1].
    
    Whilst currently unimplemented, pre-emptive scheduling requires
    additional notarization when called.  This means that future
    enhancements to Unikraft's pre-emptive scheduler will need to
    modify these methods to increase a counter within the thread
    to indicate whether the thread is pre-emptible or not.
    
    [0]: 
https://elixir.bootlin.com/linux/latest/source/include/linux/preempt.h#L169
    
    Signed-off-by: Alexander Jung <alexander.jung@xxxxxxxxx>
    ---
     include/uk/preempt.h | 40 ++++++++++++++++++++++++++++++++++++++++
     1 file changed, 40 insertions(+)
     create mode 100644 include/uk/preempt.h
    
    diff --git a/include/uk/preempt.h b/include/uk/preempt.h
    new file mode 100644
    index 0000000..d45623d
    --- /dev/null
    +++ b/include/uk/preempt.h
    @@ -0,0 +1,40 @@
    +/* SPDX-License-Identifier: BSD-3-Clause */
    +/*
    + * Authors: Alexander Jung <alexander.jung@xxxxxxxxx>
    + *
    + * Copyright (c) 2020, NEC Laboratories Europe GmbH, NEC Corporation.
    + *                     All rights reserved.
    + *
    + * Redistribution and use in source and binary forms, with or without
    + * modification, are permitted provided that the following conditions
    + * are met:
    + *
    + * 1. Redistributions of source code must retain the above copyright
    + *    notice, this list of conditions and the following disclaimer.
    + * 2. Redistributions in binary form must reproduce the above copyright
    + *    notice, this list of conditions and the following disclaimer in the
    + *    documentation and/or other materials provided with the distribution.
    + * 3. Neither the name of the copyright holder nor the names of its
    + *    contributors may be used to endorse or promote products derived from
    + *    this software without specific prior written permission.
    + *
    + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS 
IS"
    + * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, 
THE
    + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 
PURPOSE
    + * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS 
BE
    + * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
    + * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
    + * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
    + * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
    + * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
    + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF 
THE
    + * POSSIBILITY OF SUCH DAMAGE.
    + */
    +
    +#ifndef __UK_PREEMPT_H__
    +#define __UK_PREEMPT_H__
    +
    +#define preempt_disable()  barrier()
    +#define preempt_enable()   barrier()
    +
    +#endif /* __UK_PREEMPT_H__ */
    -- 
    2.11.0