Searched hist:ce0761419faefbe9e450749ccc879ff88843af12 (Results 1 – 3 of 3) sorted by relevance
/linux/arch/powerpc/net/ |
H A D | bpf_jit.h | diff ce0761419faefbe9e450749ccc879ff88843af12 Fri Sep 23 22:35:01 CEST 2016 Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> powerpc/bpf: Implement support for tail calls
Tail calls allow JIT'ed eBPF programs to call into other JIT'ed eBPF programs. This can be achieved either by: (1) retaining the stack setup by the first eBPF program and having all subsequent eBPF programs re-using it, or, (2) by unwinding/tearing down the stack and having each eBPF program deal with its own stack as it sees fit.
To ensure that this does not create loops, there is a limit to how many tail calls can be done (currently 32). This requires the JIT'ed code to maintain a count of the number of tail calls done so far.
Approach (1) is simple, but requires every eBPF program to have (almost) the same prologue/epilogue, regardless of whether they need it. This is inefficient for small eBPF programs which may not sometimes need a prologue at all. As such, to minimize impact of tail call implementation, we use approach (2) here which needs each eBPF program in the chain to use its own prologue/epilogue. This is not ideal when many tail calls are involved and when all the eBPF programs in the chain have similar prologue/epilogue. However, the impact is restricted to programs that do tail calls. Individual eBPF programs are not affected.
We maintain the tail call count in a fixed location on the stack and updated tail call count values are passed in through this. The very first eBPF program in a chain sets this up to 0 (the first 2 instructions). Subsequent tail calls skip the first two eBPF JIT instructions to maintain the count. For programs that don't do tail calls themselves, the first two instructions are NOPs.
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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H A D | bpf_jit_comp64.c | diff ce0761419faefbe9e450749ccc879ff88843af12 Fri Sep 23 22:35:01 CEST 2016 Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> powerpc/bpf: Implement support for tail calls
Tail calls allow JIT'ed eBPF programs to call into other JIT'ed eBPF programs. This can be achieved either by: (1) retaining the stack setup by the first eBPF program and having all subsequent eBPF programs re-using it, or, (2) by unwinding/tearing down the stack and having each eBPF program deal with its own stack as it sees fit.
To ensure that this does not create loops, there is a limit to how many tail calls can be done (currently 32). This requires the JIT'ed code to maintain a count of the number of tail calls done so far.
Approach (1) is simple, but requires every eBPF program to have (almost) the same prologue/epilogue, regardless of whether they need it. This is inefficient for small eBPF programs which may not sometimes need a prologue at all. As such, to minimize impact of tail call implementation, we use approach (2) here which needs each eBPF program in the chain to use its own prologue/epilogue. This is not ideal when many tail calls are involved and when all the eBPF programs in the chain have similar prologue/epilogue. However, the impact is restricted to programs that do tail calls. Individual eBPF programs are not affected.
We maintain the tail call count in a fixed location on the stack and updated tail call count values are passed in through this. The very first eBPF program in a chain sets this up to 0 (the first 2 instructions). Subsequent tail calls skip the first two eBPF JIT instructions to maintain the count. For programs that don't do tail calls themselves, the first two instructions are NOPs.
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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/linux/arch/powerpc/include/asm/ |
H A D | ppc-opcode.h | diff ce0761419faefbe9e450749ccc879ff88843af12 Fri Sep 23 22:35:01 CEST 2016 Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> powerpc/bpf: Implement support for tail calls
Tail calls allow JIT'ed eBPF programs to call into other JIT'ed eBPF programs. This can be achieved either by: (1) retaining the stack setup by the first eBPF program and having all subsequent eBPF programs re-using it, or, (2) by unwinding/tearing down the stack and having each eBPF program deal with its own stack as it sees fit.
To ensure that this does not create loops, there is a limit to how many tail calls can be done (currently 32). This requires the JIT'ed code to maintain a count of the number of tail calls done so far.
Approach (1) is simple, but requires every eBPF program to have (almost) the same prologue/epilogue, regardless of whether they need it. This is inefficient for small eBPF programs which may not sometimes need a prologue at all. As such, to minimize impact of tail call implementation, we use approach (2) here which needs each eBPF program in the chain to use its own prologue/epilogue. This is not ideal when many tail calls are involved and when all the eBPF programs in the chain have similar prologue/epilogue. However, the impact is restricted to programs that do tail calls. Individual eBPF programs are not affected.
We maintain the tail call count in a fixed location on the stack and updated tail call count values are passed in through this. The very first eBPF program in a chain sets this up to 0 (the first 2 instructions). Subsequent tail calls skip the first two eBPF JIT instructions to maintain the count. For programs that don't do tail calls themselves, the first two instructions are NOPs.
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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