Commit 9a90c83c authored by Jakub Kicinski's avatar Jakub Kicinski Committed by David S. Miller
Browse files

nfp: bpf: optimize the RMW for stack accesses 



When we are performing unaligned stack accesses in the 32-64B window
we have to do a read-modify-write cycle.  E.g. for reading 8 bytes
from address 17:

0:  tmp    = stack[16]
1:  gprLo  = tmp >> 8
2:  tmp    = stack[20]
3:  gprLo |= tmp << 24
4:  tmp    = stack[20]
5:  gprHi  = tmp >> 8
6:  tmp    = stack[24]
7:  gprHi |= tmp << 24

The load on line 4 is unnecessary, because tmp already contains data
from stack[20].

For write we can optimize both loads and writebacks away.

Signed-off-by: default avatarJakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: default avatarQuentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent a82b23fb

drivers/net/ethernet/netronome/nfp/bpf/jit.c

+25 −8
Original line number Diff line number Diff line
@@ -644,11 +644,11 @@ data_st_host_order(struct nfp_prog *nfp_prog, u8 dst_gpr, swreg offset, 


typedef int

(*lmem_step)(struct nfp_prog *nfp_prog, u8 gpr, u8 gpr_byte, s32 off,

	     unsigned int size, bool new_gpr);

	     unsigned int size, bool first, bool new_gpr, bool last);



static int

wrp_lmem_load(struct nfp_prog *nfp_prog, u8 dst, u8 dst_byte, s32 off,

	      unsigned int size, bool new_gpr)

	      unsigned int size, bool first, bool new_gpr, bool last)

{

	u32 idx, src_byte;

	enum shf_sc sc;
@@ -692,6 +692,12 @@ wrp_lmem_load(struct nfp_prog *nfp_prog, u8 dst, u8 dst_byte, s32 off, 
		reg = reg_lm(0, idx);

	} else {

		reg = imm_a(nfp_prog);

		/* If it's not the first part of the load and we start a new GPR

		 * that means we are loading a second part of the LMEM word into

		 * a new GPR.  IOW we've already looked that LMEM word and

		 * therefore it has been loaded into imm_a().

		 */

		if (first || !new_gpr)

			wrp_mov(nfp_prog, reg, reg_lm(0, idx));

	}
@@ -702,7 +708,7 @@ wrp_lmem_load(struct nfp_prog *nfp_prog, u8 dst, u8 dst_byte, s32 off, 


static int

wrp_lmem_store(struct nfp_prog *nfp_prog, u8 src, u8 src_byte, s32 off,

	       unsigned int size, bool new_gpr)

	       unsigned int size, bool first, bool new_gpr, bool last)

{

	u32 idx, dst_byte;

	enum shf_sc sc;
@@ -746,13 +752,19 @@ wrp_lmem_store(struct nfp_prog *nfp_prog, u8 src, u8 src_byte, s32 off, 
		reg = reg_lm(0, idx);

	} else {

		reg = imm_a(nfp_prog);

		/* Only first and last LMEM locations are going to need RMW,

		 * the middle location will be overwritten fully.

		 */

		if (first || last)

			wrp_mov(nfp_prog, reg, reg_lm(0, idx));

	}



	emit_ld_field(nfp_prog, reg, mask, reg_b(src), sc, shf);



	if (new_gpr || last) {

		if (idx > RE_REG_LM_IDX_MAX)

			wrp_mov(nfp_prog, reg_lm(0, idx), reg);

	}



	return 0;

}
@@ -762,6 +774,7 @@ mem_op_stack(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta, 
	     unsigned int size, u8 gpr, bool clr_gpr, lmem_step step)

{

	s32 off = nfp_prog->stack_depth + meta->insn.off;

	bool first = true, last;

	u8 prev_gpr = 255;

	u32 gpr_byte = 0;

	int ret;
@@ -777,12 +790,16 @@ mem_op_stack(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta, 
		slice_end = min(off + slice_size, round_up(off + 1, 4));

		slice_size = slice_end - off;



		last = slice_size == size;



		ret = step(nfp_prog, gpr, gpr_byte, off, slice_size,

			   gpr != prev_gpr);

			   first, gpr != prev_gpr, last);

		if (ret)

			return ret;



		prev_gpr = gpr;

		first = false;



		gpr_byte += slice_size;

		if (gpr_byte >= 4) {

			gpr_byte -= 4;

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