[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH] xen-blkfront: correct maximum segment accounting
Making use of "max_indirect_segments=" has issues: - blkfront_setup_indirect() may end up with zero psegs when PAGE_SIZE is sufficiently much larger than XEN_PAGE_SIZE - the variable driven by the command line option (xen_blkif_max_segments) has a somewhat different purpose, and hence should namely never end up being zero - as long as the specified value is lower than the legacy default, we better don't use indirect segments at all (or we'd in fact lower throughput) Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx> --- drivers/block/xen-blkfront.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) --- 4.10-rc5/drivers/block/xen-blkfront.c +++ 4.10-rc5-xen-blkfront-seg-accounting/drivers/block/xen-blkfront.c @@ -2223,7 +2223,7 @@ static int blkfront_setup_indirect(struc } else grants = info->max_indirect_segments; - psegs = grants / GRANTS_PER_PSEG; + psegs = DIV_ROUND_UP(grants, GRANTS_PER_PSEG); err = fill_grant_buffer(rinfo, (grants + INDIRECT_GREFS(grants)) * BLK_RING_SIZE(info)); @@ -2328,8 +2328,11 @@ static void blkfront_gather_backend_feat indirect_segments = xenbus_read_unsigned(info->xbdev->otherend, "feature-max-indirect-segments", 0); - info->max_indirect_segments = min(indirect_segments, - xen_blkif_max_segments); + if (indirect_segments > xen_blkif_max_segments) + indirect_segments = xen_blkif_max_segments; + if (indirect_segments <= BLKIF_MAX_SEGMENTS_PER_REQUEST) + indirect_segments = 0; + info->max_indirect_segments = indirect_segments; } /* @@ -2652,6 +2655,9 @@ static int __init xlblk_init(void) if (!xen_domain()) return -ENODEV; + if (xen_blkif_max_segments < BLKIF_MAX_SEGMENTS_PER_REQUEST) + xen_blkif_max_segments = BLKIF_MAX_SEGMENTS_PER_REQUEST; + if (xen_blkif_max_ring_order > XENBUS_MAX_RING_GRANT_ORDER) { pr_info("Invalid max_ring_order (%d), will use default max: %d.\n", xen_blkif_max_ring_order, XENBUS_MAX_RING_GRANT_ORDER); _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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