RE: Spinlocks on Uniprocessor

richard bravo <mailme_richard_linux@xxxxxxxxx> · Fri, 21 Sep 2007 02:45:06 -0700 (PDT)

In UP machines Spinlocks are compiled away, so that it only disables interrupts on spin_lock_irqsave and enables interrupts on spin_lock_irqrestore. This protects the critical section the code executing in process context and interrupt routine. Pls correct me if I am wrong.

Rajendra Stalekar <rajendra.stalekar@xxxxxxxxx> wrote:                     

  From: kernelnewbies-bounce@xxxxxxxxxxxx [mailto:kernelnewbies-bounce@xxxxxxxxxxxx] On Behalf Of jiayinjia1983116
Sent: Thursday, September 20, 2007 11:06 AM
To: Mansha Linux
Cc: kernelnewbies@xxxxxxxxxxxx
Subject: Re:Spinlocks on Uniprocessor

    As for as I know,when process/Thread is in runqueue,then may have allocate some resource even they do not running right now,In order to keep the data consistent(can not be modified by other processes/threads) ,we should use spinlock to protect the data.

    [rajendra stalekar]
 > I think that the code protected by spinlock must never have a blocking call(eg. copy_to_user, copy_from_user, read, write etc), whenever a thread acquires a spinlock whatever the critical section code has to be asynchronous and yes of course kernel must be pre-emptible.

ÔÚ2007-09-19£¬"Mansha Linux" <mansha.linux@xxxxxxxxx> £º

Hi all,

Could  you please explain me why do we need the spinlocks on uniprocessor machines?
Is this the only reason that
 the kernel is preemptive ?
-- 
regards,
Mansha 

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