On 7/12/05, Ketan Mukadam <ketanm@xxxxxxxxx> wrote: > On 7/12/05, Rik van Riel <riel@xxxxxxxxxxx> wrote: > > On Mon, 11 Jul 2005, Karane Mariano Vieira wrote: > > > > > Just a silly doubt, > > > > > > when the schedule() runs activated by the timer interrupt handler, it > > > runs in which context? interrupt context? > > > > The function schedule() is never directly activated by the > > timer interrupt handler. > > > > Instead, when the timer irq handler notices the scheduler > > should run, it sets a flag. After the irq handler has > > finished (and quit), the part of the kernel that is > > responsible for switching back to userspace mode notices > > that the flag got set. > > > > That part of the kernel, running in process context, > > then calls the scheduler. > > > > For more details about how the kernel "returns from interrupt" read > > Understanding the Linux Kernel, Second Edition > By Daniel P. Bovet, Marco Cesati > > An excellent book to clear your fundamentals about Linux. > Here is the code related to that: File: usr/src/<kernel_version>/arch/i386/kernel/entry.S#L161 161 ret_from_intr: 162 GET_THREAD_INFO(%ebp) 163 movl EFLAGS(%esp), %eax # mix EFLAGS and CS 164 movb CS(%esp), %al 165 testl $(VM_MASK | 3), %eax 166 jz resume_kernel # returning to kernel or vm86-space 167 ENTRY(resume_userspace) 168 cli # make sure we don't miss an interrupt 169 # setting need_resched or sigpending 170 # between sampling and the iret 171 movl TI_flags(%ebp), %ecx 172 andl $_TIF_WORK_MASK, %ecx # is there any work to be done on 173 # int/exception return? 174 jne work_pending 175 jmp restore_all ............ ........... ........... ............ 265 work_pending: 266 testb $_TIF_NEED_RESCHED, %cl 267 jz work_notifysig 268 work_resched: 269 call schedule On line 269 we are calling the schedule function if the $_TIF_NEED_RESCHED is set. -Gaurav > Ketan > > -- > Kernelnewbies: Help each other learn about the Linux kernel. > Archive: http://mail.nl.linux.org/kernelnewbies/ > FAQ: http://kernelnewbies.org/faq/ > > -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
