avoid vfu_log() in SGL hot path (#705)

Even though in non-debug, we don't actually log anything here, even
assembling the arguments to vfu_log() has a performance impact. Hide
them behind a DEBUG_SGL define - even in a DEBUG build, they are
particularly noisy and low-value.

Signed-off-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Swapnil Ingle <swapnil.ingle@nutanix.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/lib/dma.h b/lib/dma.h
index 089f973..be64617 100644
--- a/lib/dma.h
+++ b/lib/dma.h
@@ -288,9 +288,13 @@ dma_sgl_get(dma_controller_t *dma, dma_sg_t *sgl, struct iovec *iov, size_t cnt)
             return ERROR_INT(EFAULT);
         }
 
+#ifdef DEBUG_SGL
         vfu_log(dma->vfu_ctx, LOG_DEBUG, "map %p-%p",
                 sg->dma_addr + sg->offset,
                 sg->dma_addr + sg->offset + sg->length);
+
+#endif
+
         iov->iov_base = region->info.vaddr + sg->offset;
         iov->iov_len = sg->length;
 
@@ -326,9 +330,12 @@ dma_sgl_mark_dirty(dma_controller_t *dma, dma_sg_t *sgl, size_t cnt)
             }
         }
 
+#ifdef DEBUG_SGL
         vfu_log(dma->vfu_ctx, LOG_DEBUG, "mark dirty %p-%p",
                 sg->dma_addr + sg->offset,
                 sg->dma_addr + sg->offset + sg->length);
+#endif
+
         sg++;
     } while (--cnt > 0);
 }
@@ -358,9 +365,12 @@ dma_sgl_put(dma_controller_t *dma, dma_sg_t *sgl, size_t cnt)
             }
         }
 
+#ifdef DEBUG_SGL
         vfu_log(dma->vfu_ctx, LOG_DEBUG, "unmap %p-%p",
                 sg->dma_addr + sg->offset,
                 sg->dma_addr + sg->offset + sg->length);
+#endif
+
         sg++;
     } while (--cnt > 0);
 }