BKL: One Lock to Bind Them All

When the topic turns to the Big Kernel Lock (BKL), the comparison to Tolkien's one Ring comes naturally. The BKL was among the first locks to be created for the Linux kernel, and many other locks were developed either to complement or replace instances of it. Despite this, coders are reluctant to reduce or eliminate the usage of the BKL so while it may not rule them all, it continues, in a performance sense, to "bind them all."

Once the varied uses of the BKL are understood, the BKL can safely be replaced by other lock mechanisms, which are more appropriate for each instance. The difficulty lies in identifying these distinct instances, determining what protection is provided by the BKL in each, and carefully replacing the BKL without perturbing the rest of the system. In this paper, we examine the history of the BKL, review recent efforts to replace and remove it, and outline the work remaining. The One Lock need not rule nor bind the others any longer.

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