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e8e8a2e47d
add_interrupt_randomess always wakes up
code blocking on /dev/random. This wake up is done
unconditionally. Unfortunately this means all interrupts
take the wait queue spinlock, which can be rather expensive
on large systems processing lots of interrupts.
We saw 1% cpu time spinning on this on a large macro workload
running on a large system.
I believe it's a recent regression (?)
Always check if there is a waiter on the wait queue
before waking up. This check can be done without
taking a spinlock.
1.06% 10460 [kernel.vmlinux] [k] native_queued_spin_lock_slowpath
|
---native_queued_spin_lock_slowpath
|
--0.57%--_raw_spin_lock_irqsave
|
--0.56%--__wake_up_common_lock
credit_entropy_bits
add_interrupt_randomness
handle_irq_event_percpu
handle_irq_event
handle_edge_irq
handle_irq
do_IRQ
common_interrupt
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.