Hamish Martin <hamish.mar...@alliedtelesis.co.nz> writes: > This patch series adds the ability to configure the THREAD_SHIFT value and > thereby alter the stack size on powerpc systems. We are particularly > interested > in configuring for a 32k stack on PPC64. ... > > For instance for a 70 frame stack, the architecture overhead just for the > stack > frames is: > 70 * 16 bytes = 1120 bytes for PPC32, and > 70 * 112 bytes = 7840 bytes for PPC64. > So a simple doubling of the PPC32 stack size leaves us with a shortfall of > 5600 > bytes (7840 - (2 * 1120)). In the example the stack frame overhead for PPC32 > is > 1120/8192 = 13.5% of the stack space, whereas for PPC64 it is 7840/16384 = > 47.8% of the space. > > The aim of this series is to provide the ability for users to configure for > larger stacks without altering the defaults in a way that would impact > existing > users. However, given the inequity between the PPC32 and PPC64 stacks when > taking into account the respective minimum stack frame sizes, we believe > consideration should be given to having a large default. We would appreciate > any input or opinions on this issue.
Thanks for the detailed explanation. The patches look fine, so I don't see any reason why we wouldn't merge this. I might make the config option depend on EXPERT, but that's just cosmetic. You're right about the difference in stack overhead between 32 & 64-bit. But I guess on the other hand we've been using 16K stacks on 64-bit for over 15 years, and although we have had some reports of stack overflow they're not a common problem. cheers
