From ee591233efd57d625fea9057a975281fb8f4d358 Mon Sep 17 00:00:00 2001 From: Godbach Date: Mon, 22 Jul 2013 07:44:53 +0800 Subject: [PATCH 5/9] BUG/MEDIUM: server: set the macro for server's max weight SRV_UWGHT_MAX to SRV_UWGHT_RANGE The max weight of server is 256 now, but SRV_UWGHT_MAX is still 255. As a result, FWRR will not work well when server's weight is 256. The description is as below: There are some macros related to server's weight in include/types/server.h: #define SRV_UWGHT_RANGE 256 #define SRV_UWGHT_MAX (SRV_UWGHT_RANGE - 1) #define SRV_EWGHT_MAX (SRV_UWGHT_MAX * BE_WEIGHT_SCALE) Since weight of server can be reach to 256 and BE_WEIGHT_SCALE equals to 16, the max eweight of server should be 256*16 = 4096, it will exceed SRV_EWGHT_MAX which equals to SRV_UWGHT_MAX*BE_WEIGHT_SCALE = 255*16 = 4080. When a server with weight 256 is insterted into FWRR tree during initialization, the key value of this server should be SRV_EWGHT_MAX - s->eweight = 4080 - 4096 = -16 which is closed to UINT_MAX in unsigned type, so the server with highest weight will be not elected as the first server to process request. In addition, it is a better choice to compare with SRV_UWGHT_MAX than a magic number 256 while doing check for the weight. The max number of servers for round-robin algorithm is also updated. Signed-off-by: Godbach (cherry picked from commit a34bdc0ea402ea5be1e9d7f80eaddec772b94393) --- doc/configuration.txt | 2 +- include/types/backend.h | 4 ++-- include/types/server.h | 2 +- src/cfgparse.c | 6 +++--- src/lb_fwrr.c | 2 +- 5 files changed, 8 insertions(+), 8 deletions(-) diff --git a/doc/configuration.txt b/doc/configuration.txt index 6e0add7..a008cd7 100644 --- a/doc/configuration.txt +++ b/doc/configuration.txt @@ -1141,7 +1141,7 @@ balance url_param [check_post []] processing time remains equally distributed. This algorithm is dynamic, which means that server weights may be adjusted on the fly for slow starts for instance. It is limited by - design to 4128 active servers per backend. Note that in some + design to 4095 active servers per backend. Note that in some large farms, when a server becomes up after having been down for a very short time, it may sometimes take a few hundreds requests for it to be re-integrated into the farm and start diff --git a/include/types/backend.h b/include/types/backend.h index dc4786e..1067125 100644 --- a/include/types/backend.h +++ b/include/types/backend.h @@ -102,8 +102,8 @@ * weight modulation even with small weights (eg: 1). It should not be too high * though because it limits the number of servers in FWRR mode in order to * prevent any integer overflow. The max number of servers per backend is - * limited to about 2^32/255^2/scale ~= 66051/scale. A scale of 16 looks like - * a good value, as it allows more than 4000 servers per backend while leaving + * limited to about (2^32-1)/256^2/scale ~= 65535.9999/scale. A scale of 16 + * looks like a good value, as it allows 4095 servers per backend while leaving * modulation steps of about 6% for servers with the lowest weight (1). */ #define BE_WEIGHT_SCALE 16 diff --git a/include/types/server.h b/include/types/server.h index 14e4d1f..9fbd290 100644 --- a/include/types/server.h +++ b/include/types/server.h @@ -69,7 +69,7 @@ /* various constants */ #define SRV_UWGHT_RANGE 256 -#define SRV_UWGHT_MAX (SRV_UWGHT_RANGE - 1) +#define SRV_UWGHT_MAX (SRV_UWGHT_RANGE) #define SRV_EWGHT_RANGE (SRV_UWGHT_RANGE * BE_WEIGHT_SCALE) #define SRV_EWGHT_MAX (SRV_UWGHT_MAX * BE_WEIGHT_SCALE) diff --git a/src/cfgparse.c b/src/cfgparse.c index 345b415..7d349b3 100644 --- a/src/cfgparse.c +++ b/src/cfgparse.c @@ -3639,9 +3639,9 @@ stats_error_parsing: else if (!strcmp(args[cur_arg], "weight")) { int w; w = atol(args[cur_arg + 1]); - if (w < 0 || w > 256) { - Alert("parsing [%s:%d] : weight of server %s is not within 0 and 256 (%d).\n", - file, linenum, newsrv->id, w); + if (w < 0 || w > SRV_UWGHT_MAX) { + Alert("parsing [%s:%d] : weight of server %s is not within 0 and %d (%d).\n", + file, linenum, newsrv->id, SRV_UWGHT_MAX, w); err_code |= ERR_ALERT | ERR_FATAL; goto out; } diff --git a/src/lb_fwrr.c b/src/lb_fwrr.c index d92b6eb..7f5c8a9 100644 --- a/src/lb_fwrr.c +++ b/src/lb_fwrr.c @@ -343,7 +343,7 @@ static void fwrr_queue_srv(struct server *s) * lower the scale, the rougher the weights modulation, and the * higher the scale, the lower the number of servers without * overflow. With this formula, the result is always positive, - * so we can use eb3é_insert(). + * so we can use eb32_insert(). */ s->lb_node.key = SRV_UWGHT_RANGE * s->npos + (unsigned)(SRV_EWGHT_MAX + s->rweight - s->eweight) / BE_WEIGHT_SCALE; -- 1.8.1.5