From: Mathieu Desnoyers Date: Mon, 9 Feb 2009 17:55:09 +0000 (-0500) Subject: Raise the number of nested readers limit 2^16 and 2^32 on 32 and 64-bits arch. X-Git-Tag: v0.1~303 X-Git-Url: https://git.lttng.org/?a=commitdiff_plain;h=4917a879125c1fca08ccb4328104701e83108556;hp=4917a879125c1fca08ccb4328104701e83108556;p=urcu.git Raise the number of nested readers limit 2^16 and 2^32 on 32 and 64-bits arch. > I don't know of any code in the Linux kernel that nests rcu_read_lock() > anywhere near that deep. And if someone does find such a case, it is > pretty easy to use 15 bits rather than 8 to hold the nesting depth, just > by changing the definition of RCU_GP_CTR_BIT. > You know what ? Changing RCU_GP_CTR_BIT to 16 uses a testw %ax, %ax instead of a testb %al, %al. The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a full 8-bits, 16-bits or 32-bits bitmask for the lower order bits. On 64-bits, using a RCU_GP_CTR_BIT of 32 is also ok. It uses a testl. To provide 32-bits compability and allow the deepest nesting possible, I think it makes sense to use /* Use the amount of bits equal to half of the architecture long size */ Signed-off-by: Mathieu Desnoyers ---